Citation
Chemical recognition and swarming behavior in bats

Material Information

Title:
Chemical recognition and swarming behavior in bats
Creator:
Englert, Amy Cathleen
Publication Date:
Language:
English
Physical Description:
x, 70 leaves : ; 28 cm

Thesis/Dissertation Information

Degree:
Master's ( Master of science)
Degree Grantor:
University of Colorado Denver
Degree Divisions:
Department of Integrative Biology, CU Denver
Degree Disciplines:
Biology

Subjects

Subjects / Keywords:
Tadarida brasiliensis -- Behavior ( lcsh )
Animal communication ( lcsh )
Bats -- Flight ( lcsh )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references (leaves 66-70).
General Note:
Department of Integrative Biology
Statement of Responsibility:
by Amy Cathleen Englert.

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Source Institution:
|University of Colorado Denver
Holding Location:
Auraria Library
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
319832052 ( OCLC )
ocn319832052
Classification:
LD1193.L45 2008m E53 ( lcc )

Full Text
CHEMICAL RECOGNITION AND SWARMING BEHAVIOR IN BATS
by
Amy Cathleen Englert
B.S. Biology, Colorado State University, 2006
A thesis submitted to the
University of Colorado Denver
in partial fulfillment
of the requirements for the degree of
Master of Science
Biology
2008


This thesis for the Master of Science
degree by
Amy Cathleen Englert
has been approved
by
Michael J. Greene
Greg Cronin
Cheri A. Jones


Englert, Amy C. (Master of Science, Biology)
Chemical Recognition and Swarming Behavior in Bats
Thesis directed by Assistant Professor Michael J. Greene
ABSTRACT
Little is known about the social behavior in temperate Microchiropteran bats,
especially in regards to chemical communication and autumn swarming. The
purpose of this study is to use an assimilation of data from controlled and field
studies to draw relationships between roosting behavior, chemical
communication, and environmental conditions. Captive studies were designed to
test the response of captive Tadarida brasiliensis to odors produced by
conspecifics. Though bats did not respond to odors on swabs, and showed little
roosting preferences for individuals within established colonies, they did show a
strong preference for roosting in roosting pouches emitting the odors of familiar
individuals as compared to neutral roosting pouches and roosting pouches
emitting the odors of unfamiliar bats. Field studies were designed to gather
observational data to elucidate the variations in autumn swarming behavior at one
site in Garfield County, Colorado. Variations in bat activity throughout each
night and the season were calculated, and correlated with environmental variables
such as temperature, humidity, light intensity, and cloud cover. These data are
important because there have been no previous studies of swarming behavior at
this site, and they help to counter the paucity of swarming data in this region.
This abstract accurately represents the content of the candidates thesis. I
recommend its publication.
Signed
Michael J. Greene


ACKNOWLEDGMENT
My thanks to my advisor, Michael Greene for his invaluable advice and guidance.
I would also like to thank Barbara French and Amanda Lollar for the use of their
bat colonies for captive studies, and Kirk Navo of the Colorado Division of
Wildlife for assistance with experimental design and the use of data. Lastly, I
would like to thank Ian Moore, Tim Englert, Greg Englert, and Philip Englert for
their assistance in the field.


TABLE OF CONTENTS
Figures...............................................................viii
Tables...................................................................x
Chapter 1
1. Introduction........................................................1
2. Methods.............................................................5
2.1 Research Models and Study Locations.................................5
2.2 Captive Conditions..................................................5
2.3 Experiment 1: Testing the Response of Captive Bats to the
Glandular Secretions of Conspecifics................................7
2.4 Experiment 2: Testing Whether Bats in a Small Captive Colony
Show a Preference for Roosting with Specific Colony Members.........8
2.5 Experiment 3: Testing Whether Bats Use a System of Chemical
Recognition of Roostmates to Choose Roost Sites.....................8
3. Results............................................................16
3.1 Experiment 1: Testing the Response of Captive Bats to the
Glandular Secretions of Conspecifics...............................16
3.2 Experiment 2: Testing Whether Bats in a Small Captive Colony
Show a Preference for Roosting with Specific Colony Members........16
3.3 Experiment 3: Testing Whether Bats Use a System of Chemical
Recognition of Roostmates to Choose Roost Sites....................16
3.3.1 Analysis 1: Rejection of Pouches..................................17
v


3.3.2 Analysis 2: Number of Bats Entering Pouches and Number of
Incidences of Entering Pouches....................................17
4. Discussion........................................................24
4.1 Summary...........................................................24
4.2 Experiment 1: Testing the Response of Captive Bats to the
Glandular Secretions of Conspecifics .............................24
4.3 Experiment 2: Testing Whether Bats in a Small Captive Colony
Show a Preference for Roosting with Specific Colony Members.......24
4.4 Experiment 3: Testing Whether Bats Use a System of Chemical
Recognition of Roostmates to Choose Roost Sites...................25
4.5 Significance of Research..........................................27
Bibliography ..........................................................29
Chapter 2
1. Introduction......................................................32
2. Methods...........................................................40
2.1 Research Models and Study Locations...............................40
2.2 Experiment 1: Cataloging the General Activity Patterns of Autumn
Swarming Behavior.................................................40
2.3 Experiment 2: Testing Whether Abiotic Environmental Factors Affect
Swarming Behavior.................................................41
3. Results...........................................................44


3.1 Nightly Patterns.....................................................44
3.2 Seasonal Patterns....................................................46
4. Discussion...........................................................60
4.1 Summary..............................................................60
4.2 Nightly Patterns.....................................................60
4.3 Seasonal Patterns....................................................61
4.4 Significance of Research.............................................64
Bibliography ............................................................66


LIST OF FIGURES
Figure
1 The Research Model.................................................4
2 Schematic of Female Roosting Cage and Roosting Pouch
Numbers in Colony B...............................................11
3 Roosting Cage and Roosting Pouches................................12
4 Schematic of Cotton Swab Placement in the Testing Arena for
Experiment One....................................................13
5 Pouch Rejection by Tadarida brasiliensis..........................19
6 Pouch Choice by Tadarida brasiliensis.............................20
7 Groaning Cave Location............................................43
8 Swarming Study Activity Rate......................................48
9 Swarming Study Activity Level 1 ..................................49
10 Swarming Study Activity Level 2...................................50
11 Seasonal Activity Rate and Level..................................51
12 Seasonal Activity Rate (Bats Per Minute) and Cave
Temperature (Celsius).............................................52
13 Seasonal Activity Rate (Bats Per Minute) and Outside
Temperature (Celsius).............................................53


14 Seasonal Activity Rate (Bats Per Minute) and Cave
Relative Humidity (%).................................................54
15 Seasonal Activity Rate (Bats Per Minute) and Outside
Relative Humidity (%).................................................55
16 Seasonal Activity Rate (Bats Per Minute) and Air
Pressure (mmHg).......................................................56
17 Seasonal Activity Level (Bats Per Frame) and Cave
Temperature (Celsius).................................................57
18 Seasonal Activity Level (Bats Per Frame) and Cave
Relative Humidity (%).................................................58
IX


LIST OF TABLES
Table
1 Ethogram of experiment one behaviors................................14
2 Barbara Frenchs (colony B) bat identification key used
in experiment one to identify individual bats.......................15
3 Number of times in which each bat roosted with other
specific individuals in the male cage...............................21
4 Number of times in which each bat roosted with other
specific individuals in the female cage.............................22
5 Number of times in which each bat roosted with other
specific individuals in the geriatric cage..........................23
6 Table of species documented at the swarm at Groaning Cave...........39
7 Summary table of cave data by night.................................59
x


Chapter 1
Chemical Recognition of Roostmates in Tadarida brasiliensis


1. Introduction
Bat species, especially those that live in colonies, rely on complex social cues
created by the combination of chemical and vocal stimuli. Bats use
semiochemicals to mediate activities including: 1) foraging (Bloss 1999; Page
and Ryan 2006), 2) roosting (Bloss et al. 2002; Bouchard 2001; De Fanis and
Jones 1995; Heideman et al. 1990), 3) mating (Crichton and Krutzsch 2000;
Voight 1998; Voight and Von Helverson 1999), and 4) female-pup interactions
(Gustin and McCracken 1987; Loughry and McCracken 1991).
Roostmate recognition, the focus of this study, is important because many
species are philopatric, forming stable associations within closed colonies or
harems (Bloss et al. 2002; Burland et al. 1999; Kerth et al. 2000; Kerth et al.
2002; Veith et al. 2004; Voight and Von Helverson 1999). Bats that live in a
group often exhibit a group scent profile in addition to an individual scent
profile which can be used for identification by other individuals (Bloss 1999).
Scent profiles can be created by a combination of scents produced by glandular
secretions, urine, feces, and the microbial action of bacterial communities
(Nielson et al. 2006). Bats can distinguish between roostmates and non-
roostmates, between males and females, and individuals of different age based
on scent alone (Bloss et al. 2002; Bouchard 2001; De Fanis and Jones 1995).
When female Big Brown Bats (Eptesicus fuscus) are presented with olfactory
stimuli alone, all will choose to follow the scent of roostmates over non-
roostmates in a y-maze on the first trial, and in 77% of subsequent trials (Bloss
et al. 2002). In a similar experiment, Common Pipistrelles {Pipistrellus
pipistrellus) chose the scent of roostmates over unfamiliar bats 75-100% of the
time (De Fanis and Jones 1995). Little Brown Bats (Myotis lucifugus) also are
reported to recognize colony-mates and to touch noses briefly when meeting
other bats, perhaps to come into closer contact with the facial glands on the
muzzle (Bloss 1999).
Bloss et al. (2002) suggested that a unique colony profile smell could be created
by a combination of similar diet and roosting substrate, grooming behaviors to
spread secretions, exposure to the same microbial communities, and the fact that
colony members are often genetically related. The Mexican Free-tailed Bat
(Tadarida brasiliensis) produces a chemical which distinguishes its scent profile
from that of other species of bats. The principle odorant in colonies of T.
brasiliensis, 2-aminoacetophenone, is a polar molecule that strongly binds to
1


substrate materials and dust particles, and therefore will permeate the roost and
dust in the surrounding air (Nielson et al. 2006). The hypothesis that bats use a
colony profile scent to identify roostmates (De Fanis and Jones, 1995) seems a
more parsimonious explanation for this behavior in T. brasiliensis than the
suggestion that bats are recognizing familiar bats from individual scents (Bloss
et al. 2002; Bouchard 2001), namely because of the millions of individuals that
make up some colonies. The findings of Bloss et al. (2002) support the
hypothesis that scents from different colonies of E. fuscus can be differentiated
using gas chromatograms, evidence that colony profiles can be chemically
distinct.
There is evidence that chemical communication is used extensively in bats to
mediate social interactions, but little is known about how chemical signals might
affect roosting choices (Bloss 1999; Dechmann and Safi 2005; Voigt and von
Hel verson 1999). The first part of this study examines whether a
microchiropteran, the Mexican Free-tailed Bat (71 brasiliensis) has the ability to
distinguish between familiar roostmates and unfamiliar non-roostmates based on
scent alone. Based on previous research demonstrating individual recognition in
females and pups in this species (Gustin and McCracken 1987; Loughry and
McCracken 1991) and the general complexity of their social interactions, I
predicted that T. brasiliensis has the ability to distinguish roostmates from non-
roostmates based on chemical cues. Tadarida brasiliensis (Figure 1) is an ideal
research model for this study, because it is a gregarious species which has a
unique and pungent scent profile and females have the ability to recognize
individuals chemically (Gustin and McCracken 1987; Loughry and McCracken
1991).
I tested the following hypotheses in this experiment:
1. Individuals will demonstrate investigative or antagonistic behavioral
responses to cotton swabs containing the chemical secretions of
conspecifics.
2. Individuals within a captive colony will preferentially roost with other
individuals in the colony.
3. Individuals will demonstrate the ability to distinguish between
roostmates and non-roostmates using chemical cues alone.
2


The study of chemical communication is vital to the understanding of bat
behaviors ranging from foraging and roosting to mating and pup-rearing. There
have been only a few preliminary studies of this behavior to date (Bloss 1999;
Gustin and McCracken 1987; Loughry and McCracken 1991). Populations of
bats which are threatened cannot be managed effectively without an
understanding of colony dynamics and roost choice, topics that can begin to be
addressed through study of chemical communication among conspecifics.
3


Figure 1: The Research Model. Two female Tadarida brasiliensis from colony
B, demonstrating the general appearance and size of this species.
4


2. Methods
2.1 Research Models and Study Locations
Chemical communication studies were carried out using two colonies of
rehabilitated T. brasiliensis maintained by Barbara French (Bat Conservation
International, P.O. Box 162603 Austin, TX 78716), and Amanda Lollar (Bat
World Sanctuary, 217 N. Oak Ave. Mineral Wells, TX 76067). Completion of
research at both locations was authorized and aided by both Barbara French and
Amanda Lollar, whose mission is the rehabilitation of injured and orphaned
bats, the release or long-term care of rehabilitated bats, and education of the
public. These two colonies are useful for behavioral studies because
unreleasable bats are kept captive permanently, individuals are habituated to
human handling, and the two distinct colonies are within driving distance from
each other.
Tadarida brasiliensis is a medium-sized microchiropteran with a mass of
approximately 11-14 grams and a wingspan of about 30 centimeters (Adams
2004). These bats characteristically feed on a wide variety of insects which they
obtain by utilizing echolocation. Tadarida brasiliensis is common in the
southern U.S. and Mexico, and is well known for maternity colonies exceeding
millions of individuals in size (Loughry and McCracken 1991). Most bats used
in the study were rehabilitated wild bats unsuitable for release, though a few
were bom in captivity. However, all bats were mobile, exhibited normal
behaviors, and were capable of performing in behavioral experiments. This
species is useful for behavioral choice studies because it is small and relatively
docile, and has complex social interactions, some of which have been shown to
be mediated by odors, related to large colonial sizes (Gustin and McCracken
1987; Loughry and McCracken 1991).
2.2 Captive Conditions
Bats in the colony maintained by Amanda Lollar (hereinafter referred to as
colony A) were all housed together in an open roosting cage (approximately 1 x
1.5 x 0.5 meters) within a larger enclosed indoor flight cage (approximately 3 x
3x8 meters) which contained about fifty T. brasiliensis. Roosting pouches
were attached to the walls and ceiling of the cage, and all bats were free to move
throughout the cage. Temperature was controlled by air conditioning and
5


heating, and light intensity was kept dim during the day and dark at night. The
bats were given free access to live mealworms, and if needed were hand-fed
mealworms or a blended mixture of mealworms, vitamins, and baby food up to
twice daily.
The bats in the colony maintained by Barbara French (hereinafter referred to as
colony B) were housed in three cages based on age and sex within a small
climate-controlled bam. In one enclosure, nine adult females and two juvenile
females were housed in an open wooden roosting cage with thirty cloth roosting
pouches attached to the sides and ceiling (Figure 2 and Figure 3). Roosting
pouches consisted of thick padded, quilted cotton doubled and then sewn on two
of the three edges to produce a small pouch that is open on one end (Figure 3).
The bats normally roost inside, underneath, or behind roosting pouches.
Pouches are about 15 x 20 x 5 centimeters and can house eight to ten bats
(Source: Bat World Sanctuary, www.batworld.org). In a second enclosure,
seven adult males and one juvenile male were housed in a closed wooden
roosting cage with thirteen roosting pouches on the walls and ceiling and one on
the floor of the cage (Figure 2). In a third enclosure, two geriatric female T.
brasiliensis were housed with a geriatric male Cave Bat (Myotis velifer) and a
geriatric male Evening Bat (Nycticeius humeral is) in a small closed wooden
roosting cage with four cloth roosting pouches on the walls and one on the floor
(Figure 2). Geriatric bats were visibly older and less active than other bats in the
colony, and were considered to be geriatric on the basis of tooth wear.
All three cages had a small heating pad covered with a cloth towel on the floor.
The bam was kept cool in the summer months by an air conditioning unit. The
availability of the heating pad allowed the bats to choose a warmer roosting
temperature, and it was covered with a towel to provide a dark, private roosting
space. The bam was cooler than ambient temperature during the day, and
roughly equaled ambient night temperatures in July. Light conditions inside the
bam were kept uniformly dim through the day and night by covering the
windows and providing dim artificial lighting. Bats were fed either whole live
mealworms or a blended mixture of mealworms, vitamins, and baby food ad
libitum. Although water and both food types constantly were available, each bat
was also hand-fed nightly. All bats used in experimental trials were either
captive bom or sufficiently recovered from any past injuries to enable them to
move and feed adequately, and to make behavioral choices.
6


2.3 Experiment 1: Testing the response of captive bats to the glandular
secretions of conspecifics
This experiment was designed to test the hypothesis that captive Mexican Free-
tailed Bats discriminate between glandular secretions from familiar and
unfamiliar individuals of the same species. Glandular secretions were collected
from both adult and juvenile males and females from colony A and colony B.
One-ended cotton swabs were rubbed on the face, under the chin, on the gular
gland (when present), and on the urogenital area of the Free-tails for two to three
minutes and then placed in labeled plastic vials, which were then sealed and
refrigerated until use at a temperature of approximately 3 degrees Celsius.
Abbreviations used for labeling are given in Figure 4.
I used a 45.72 x 66.04 x 60.96 centimeter testing arena made of cloth along the
bottom and black mesh stretched tightly around a PVC pipe frame. The arena
was a cage usually used to house orphaned T. brasiliensis or Eastern Red Bats
(Lasiurus borealis). The arena was wiped down inside and out with 50%
isopropyl alcohol solution before use and between each trial in an attempt to
remove residual odors.
Two lengths of measuring tape (cloth craft tape) were cut to size and taped with
surgical tape to the floor of the testing arena perpendicular to each other so the
bats could be released exactly in the middle of the arena in each successive trial.
The testing arena was placed within a large outdoor flight cage where all trials
were conducted on three successive nights. Fifteen bats were randomly chosen
from colony B, which were tested one at a time in the testing arena. Barbara
chose one bat from either the male or female population and brought it to the
large flight cage in a small mesh transport cage. The bat was then placed in the
middle of the testing arena under a paper towel and monitored for a thirty-
minute data collection period. One cotton swab with each type of collected
secretion (juvenile male, adult male, juvenile female, and an adult female) from
colony A and colony B, as well as a clean cotton swab used as a control, were
tied with string to the side of the cage approximately 7.5 centimeters from the
floor (Figure 4). To randomize placement of cotton swabs in the cage, a vial
containing a cotton swab of each type was placed in a plastic bag, and one vial
was drawn randomly from the bag to be tied in each position.
7


Activity of the focal bats was recorded using a Sony Nightshot DCR-SR62
mounted on a tripod. Sufficient light for observation and recording was
provided by three black lights suspended from the ceiling of the flight cage to
attract insects. I classified activity during the thirty-minute period into three
behavioral types relating to the cotton swab based on an a priori ethogram
(Table 1). Bats could show 1} investigative behavior towards the cotton swab,
characterized by lingering, sniffing, marking, visually examining, or making
vocalizations directed towards the cotton swabs, 2} antagonistic behaviors
characterized by attacking the cotton swabs, or 3} no response, characterized
by a lack of any discemable behaviors directed towards the cotton swabs. The
average amount of time spent performing each behavior was recorded for each
bat. The ethogram was developed using normally observed bat behaviors as a
guideline.
After the thirty-minute observation period, the bat was removed from the cage
and returned to the bat bam in a transport container, and the cage was wiped
down completely with 50% isopropyl alcohol solution. Cotton swabs were
changed between trials if bats had contacted them directly.
2.4 Experiment 2: Testing whether bats in a small captive colony show a
preference for roosting with specific colony members
This experiment was designed to test the hypothesis that captive T. bras Mens is
preferentially and consistently will roost with certain colony-mates. This
experiment was observational in nature, involving recording the location in the
roosting cages of each bat in the colony twice daily. Generally, roosting
locations were recorded six to twelve hours apart, once at mid-day and once at
night. The bats were identified by Barbara French using unique marks and scars
(Table 2). Each pouch in a cage was assigned a numerical value (Figure 2).
Data were analyzed using a G-test for goodness of fit using two-tailed P values
because no predictions were made.
2.5 Experiment 3: Testing whether bats use a system of chemical
recognition of roost mates to choose roost sites
This experiment was designed to test the hypothesis that bats are able to
discriminate between the scents of familiar and unfamiliar conspecifics when
8


making roosting choices. 12 x 17 centimeter pieces of black felt were used to
absorb bat scents from each colony. Fifty felt pieces were given to Amanda
Lollar to place in the roosting pouches in colony A. The felt was left in the
roosting pouches with both sexes of bats for a period of five days and then
stored in a sealed plastic bag at 3 Celsius for two days. Fifty pieces of felt were
also given to Barbara French (colony B) on the same day, and were placed in
each of the thirty roosting pouches in the female cage and fourteen pouches in
the male cage, where they were left for a period of five days and then placed in
sealed labeled bags and refrigerated at approximately 3 Celsius. The remaining
fifty felt pieces were placed in a labeled sealed bag and stored separately at 3
Celsius to serve as clean controls. Because all of the bats belonged to the same
species, were from the same geographical area, subsisted on similar diets, and
lived in similar captive conditions, placing the felt pieces in each colony allowed
the collection of scents that could be recognized as originating from familiar and
unfamiliar conspecifics by test bats. All trials in experiment 3 were completed
using bats from colony A as the focal animals.
A small cage (approximately 70 x 40 x 40 centimeters) was used as the testing
arena for this experiment. The cage consisted of black mesh stretched around a
PVC frame. The cage was placed within an indoor flight cage. At the
beginning of trial one, three clean cloth roosting pouches were obtained. Two
pieces of clean felt were placed in one, two pieces of felt from colony B (i.e.
unfamiliar scent) were placed in the second, and two pieces of felt from
colony A (i.e. familiar scent) were placed in the third. The pouches were then
randomly placed in three of the four comers of the mesh cage, and a bat
randomly chosen from a transport container was released in the middle of the
cage, facing away from the observer. I recorded the behavior of each bat for a
thirty-minute period using incidental light, and the muted light of a small
flashlight to track the bats within the cage. After each trial, the felt pieces were
discarded and replaced, new felt pieces were placed randomly in one of the three
pouches, and the pouches again were placed in a random orientation in three
comers of the cage. Although the same pouches were used in all experimental
trials, the pouches were replaced if urine or guano was present after the trial, and
pouches were randomized between trials. The stronger odor on the felt acted as
the stimulus for the bats in this case.
The number of bats and number of incidences in which bats entered each pouch,
burrowed under or behind each pouch, and rejected each pouch was then
9


recorded during the thirty-minute trial. Bats were considered to have rejected a
pouch if they approached the pouch entrance, stopped, and clearly investigated
the entrance before refusing to enter the pouch. The number of incidences of
each type was a tally of the total number of times that any activity occurred,
while the number of bats that exhibited the behavior was recorded as the last
choice that each bat made during the course of the trial.
Trials in which bats appeared to be alarmed by handling, or those in which bats
moved directly to one location in the testing arena after being released and
stayed at that location for the entirety of the trial, were excluded from analysis.
Bats which were stressed did not have an opportunity to make a true choice
among the stimuli in the behavioral experiment. These criteria resulted in six
bats and six incidences being excluded from the analysis. Data were analyzed
using a Chi squared test for goodness of fit, and Chi squared pairwise
comparisons with a Bonferroni correction using one-tailed P values because the
results were consistent with the a priori hypothesis.
10


a.
Lett Wall
(eilina
Rialit Outside Wall
Heating Pad Floor
14
5 16
b.
Left Wall Back Wall Right Wall
C.
Left Wall Back Wall
s
Floor
Heating Pad
Right Wall
m
Figure 2: a. Schematic of Female Roosting Cage and Roosting Pouch Numbers
in Colony B. b. Schematic of Male Roosting Cage and Roosting Pouch
Numbers in Colony B. c. Schematic of Geriatric Roosting Cage and Roosting
Pouch Numbers in Colony B. Each number represents one pouch attached to the
wall or ceiling of the roosting cage. These pouch numbers were used to record
bat roosting preferences for experiment 2.
11


Figure 3: Roosting Cage and Roosting Pouches, a. Picture of female roosting
cage in colony B. This is where bats in colony B normally roost, b. Cloth
Roosting Pouches. These pouches were hung in the roosting cages in colony A
and colony B. Bats roost in them under normal conditions by crawling in,
under, or behind them. Source: www.utexas.edu
12


JM = Juvenile Male
AM = Adult Male
JF = Juvenile Female
AF = Adult Female
-A = Amanda's Colony
-B = Barbara's Colony
Figure 4: Schematic of Cotton Swab Placement in the Testing Arena for
Experiment One. Sex/age abbreviations used to assign bat numbers are on the
right of the figure. Numbers next to cotton swabs were used to identify the
position of each scent.
13


Table 1: Ethogram of experiment one behaviors. Bat behaviors in experiment
one were assessed and recorded using the behaviors listed.
Behavior Type Typical Behaviors
Investigative Lingering, sniffing, marking, visually examining, or making vocalizations directed towards the cotton swabs
Antagonistic Attacking the cotton swabs
No Response No behaviors directed towards the cotton swabs
14


Table 2: Barbara Frenchs (colony B) bat identification key used in experiment
2 to identify individual bats. This table records all of the unique scars and
markings which are used to identify rehabilitated bats in colony B. This
demonstrates that Barbara French is able to reliably identify each bat in the
colony.
Bat# Bat Name Identifying Characteristics
AF1 Betty Davis Very brown. Injury to left second finger.
AF2 Chocolate Cesarean Section scar on abdomen.
AF3 Daphne Missing many teeth on bottom jaw.
AF4 Kisi Deformed left forearm (from fracture) and scar from banding as a pup.
AF5 Kitty Red swellings above each eye.
AF6 Molly White around the ears.
AF7 Polly Pale scar on left wing membrane.
AF8 Precious No identifying marks (the onlv one without anv). Larger ears than Molly.
AF9 Roxy Missing one tooth on bottom jaw, and severe staining of teeth. Cesarean Section scar on abdomen.
JF1 Daisy Much smaller and darker than the others. Cartilage still present in the metacarpal phalangeal joint.
JF2 Vanilla Larger and paler of the juveniles.
AMI Arm Conspicuous injury' to right forearm large knob of bone present.
AM2 Doc Two amputated fingers from right wing (second and third phalanges), and weepy right eye.
AM3 Mr. White Dark fur with a lighter head. Forearm deformity (from fracture) on right wing from banding as a pup.
AM4 Nick Very skinny, needs to be hand fed.
AM5 Slim Tip of left and right wing membranes missing between the third and fourth phalanges.
AM6 Scarface Bald patch under chin.
AM7 Two-Tone Brown along midline and charcoal gray peripherally.
JM1 Squirt Very small compared to the others. Very dark in color. Some cartilage still present in the metacarpal phalangeal joint.
GF1 Amanda Large hole in right wing.
GF2 Lizzie Borden Entire right wing amputated.
GM1 Curly Myotis velifer
GM2 Jasper Nycticeius humeralis
15


3. Results
3.1 Experiment 1: Testing the response of captive bats to the glandular
secretions of conspecifics
Captive T. brasiliensis from Colony B did not exhibit a reaction to the swabs
containing glandular secretions from conspecifics with the exception of a single
male (AM7-B), who sniffed a swab taken from a female he had mated with in
previous seasons. This behavior would be classified according to the ethogram
provided in the previous section as investigative.
3.2 Experiment 2: Testing whether bats in a small captive colony show a
preference for roosting with specific colony members
Most bats in the experiment roosted randomly with other conspecific individuals
in the colony. A few bats associated with other bats at roosting sites; there was
a small number which strongly preferred association with specific individuals.
Each time a bat roosted with another bat, it was given a score of one, and the
score for each pair of bats was then summed. The average number of all events
in which bats were found roosting with another bat was calculated and used as
the expected value in a statistical test. The observed scores were compared to
the average score using a G-test for goodness of fit with 2-tailed values. For
most of the bats, there was not a statistically significant difference in the amount
of time a particular bat spent roosting with another, with a few exceptions.
Among the males, bat JM1-B was significantly more likely to be roosting with
AM1-B (G = 6.23,p = 0.0126) or AM3-B (G = 12.90,= .0003) than expected
by chance. Bats AM5-B and AM7-B also were significantly more likely to be
roosting with each other than with any other individual. (G = 6.23, p = 0.0126)
(Table 3). Among the females, bat AF4-B was significantly more likely to be
roosting with both JF1 -B (G = 5.189, p = .0227) and JF2-B (G = 5.189, p =
.0227). JF1-B and JF2-B were significantly more likely to be roosting with each
other (G = 5.189, p = .0227) than with any other bats (Table 4). Among the
geriatric bats, GF1-B and GM1-B were significantly more likely to be roosting
with each other than alone or with other bats (G = 16.163,p< 0.0001) (Table 5).
3.3 Experiment 3: Testing whether bats use a system of chemical
recognition of roost mates to choose roost sites
16


3.3.1 Analysis 1: Rejection of pouches.
Individuals were able to discriminate between the odor of familiar roostmates
and unfamiliar non-roostmates, demonstrated by the number of bats which
rejected pouches, and the number of incidences in which pouches were rejected.
I defined rejection as a bat moving towards a pouch, pausing at the entrance,
then moving away and failing to enter the pouch during the trial. No individual
rejected a pouch more than once, so the number of bats and number of
incidences were the same for this parameter. There were significant differences
in number of rejections among experimental treatments (X2 = 7.001,/? = 0.0151)
(Figure 5). Bats rejected unfamiliar pouches more than familiar pouches (X2 =
5.000, /? = 0.0127, Bonferroni corrected a = 0.017). There was no significant
difference in the rejection rates between familiar and control pouches (X2 =
1.000, /? = 0.15, Bonferroni corrected a = 0.017) or unfamiliar pouches and
control pouches (X2 = 2.667,/? = 0.051, Bonferroni corrected a = 0.017).
3.3.2 Analysis 2: Number of bats entering pouches and number of
incidences of entering pouches.
There was a significant difference in the number of bats which chose to enter
pouches among experimental treatments (X2 = 10.776,/? = 0.0023). Bats
preferred the familiar pouch over the unfamiliar pouch (X2 = 7,/? = 0.00041,
Bonferroni corrected a = 0.017) or the control pouch (X2 = 4.5,/? < 0.01695,
Bonferroni corrected a = 0.017). There was no significant difference in
discrimination between the unfamiliar pouch and the control pouch (X2 = 1.000,
/? = 0.1587, Bonferroni corrected a = 0.017).
There was a significant difference in the number of bats which burrowed under
or behind familiar, unfamiliar, and control pouches (X2 = 7.4027,/? = 0.01235).
Bats burrowed under or behind the familiar pouch more often than the control
pouch (X2 = 7,p = 0.00041, Bonferroni corrected a = 0.017), but there was no
significant discrimination between the familiar and unfamiliar pouches (X2 =
4.0774,/? = 0.02175, Bonferroni corrected a = 0.017) or the unfamiliar and the
control pouches (X2 = 3,p = 0.04165, Bonferroni corrected a = 0.017) using this
measure.
The number and incidences in which bats went in, under, or behind pouches
were combined because the stimulus was present in all three cases, and bats
17


were observed to enter and burrow under and behind the pouches in the course
of normal roosting behavior. There was a significant difference in the number
of bats which went in, under, or behind the pouches among the experimental
treatments (X2 = 15.396,/? = 0.00025) (Figure 6). More bats went in, under, or
behind the familiar pouch than the unfamiliar pouch (X2 = 8.333, p = 0.00195,
Bonferroni corrected a = 0.017) or the control pouch (X2 = 8.333,/? = 0.00195,
Bonferroni corrected a = 0.017). There was no significant discrimination
between the unfamiliar and control pouches (X2 = 0,/? = 0.5, Bonferroni
corrected a = 0.017).
There was a statistically significant difference in the number of incidences in
which bats chose to enter pouches among the experimental trials (X2 = 17.38,/?
= 0.0001) (Figure 3.2). Bats entered the familiar pouch in more incidences than
the unfamiliar pouch (X2 = 13,/? = 0.00015, Bonferroni corrected a = 0.017) or
the control pouch (X2 = 6.25,/? = 0.0124, Bonferroni corrected a = 0.017). There
was no difference in discrimination between the unfamiliar and control pouch
(X2 = 1.5,/? = 0.04165, Bonferroni corrected a = 0.017).
There was also a statistically significant difference in the number of incidences
in which bats chose to burrow under or behind pouches among the experimental
trials (X2 = 8.94, p 0.0057). Bats burrowed under or behind the familiar pouch
in more incidences than the control pouch (X2 = 8.333, p 0.00195, Bonferroni
corrected a = 0.017). There was no significant difference in discrimination
between the familiar and unfamiliar pouches (X2 = 2.25,/? = 0.0668, Bonferroni
corrected a = 0.017) or the unfamiliar and control pouches (X2 = 2.667, p =
0.05125, Bonferroni corrected a = 0.017) in the number of incidences.
There was a significant difference in the number of incidences in which bats
went in, under, or behind pouches among the experimental treatments (X2 =
23.091,/? < 0.0001) (Figure 6). Bats went in, under or behind the familiar pouch
in more incidences than the unfamiliar pouch (X2 = 12.448,/? = 0.0002,
Bonferroni corrected a = 0.017) or the control pouch (X2 = 14.2857,/? = 0.0001,
Bonferroni corrected a = 0.017). There was no significant discrimination
between the unfamiliar and control pouch in this experiment (X2 = 0.111,/? =
0.3695, Bonferroni corrected a = 0.017).
18


Figure 5: Pouch rejection by T. brasiliensis. The number of bats and number of
incidences was the same for this parameter, thus the figure represents both
number of bats which rejected pouches and number of incidences in which
pouch rejection occurred. Differences in letters above bars denote statistical
significance between treatments using a Chi squared pairwise comparison with a
Bonferroni correction (Bonferroni corrected alpha = 0.017). Bats reject (refuse
to enter) unfamiliar pouches more often than familiar pouches.
19


a.
Figure 6: Pouch Choice by T. brasiliensis. a. Number of T. brasiliensis which
entered or burrowed under or behind each type of pouch. Bats burrow under or
behind familiar pouches more than unfamiliar or control pouches, b. Number of
incidences in which T. brasiliensis entered or burrowed under or behind each
pouch type. Bats burrowed under of behind familiar pouches in more incidences
than unfamiliar or control pouches. Differences in letters above bars denote
statistical significance between treatments using a Chi squared pairwise
comparison with a Bonferroni correction (Bonferroni corrected alpha = 0.017).
20


Table 3: Number of times in which each bat roosted with other specific
individuals in the male cage. The row and column headers indicate bat
identification numbers. Starred values indicate P value significance using a G-
test for Goodness of Fit (alpha = 0.05). Several bats in the male cage
demonstrated a preference for roosting with specific individuals.
AMI AM2 AM3 AM4 AM5 AM6 AM7 JM1
AMI 4 4 3 2 4 3 6*
AM2 2 4 3 2 4 3
AM3 3 5 5 2 8*
AM4 4 1 4 3
AM5 1 6* 5
AM6 1 5
AM7 3
JM1
21


Table 4: Number of times in which each bat roosted with other specific
individuals in the female cage. The row and column headers indicate bat
identification numbers. Starred values indicate P value significance using a G-
test for Goodness of Fit (alpha = 0.05). Several bats in the female cage
demonstrated a significant preference for roosting with specific individuals.
AF1 AF2 AF3 AF4 AF5 AF6 AF7 AF8 AF9 JF1 JF2
AF1
AF2 10 9 9 9 10 10 11 9 9
AF3 8 8 8 10 9 10 8 8
AF4 9 10 10 11 10 12* 12*
AF5 8 8 10 10 9 9
AF6 10 9 9 10 10
AF7 9 10 10 10
AF8 11 11 11
AF9 10 10
JF1 12*
JF2

22


Table 5: Number of times in which each bat roosted with other specific
individuals in the geriatric cage. The row and column headers indicate bat
identification numbers. Starred values indicate P value significance using a G-
test for Goodness of Fit (alpha = 0.05). Two of the bats in the geriatric cage
demonstrated a significant preference for roosting with each other.
GF1 GF2 GM1 GM2
GF1 1 9*
GF2 1
GM1
GM2
23


4. Discussion
4.1 Summary
1. In this experiment, individual Tadarida brasiliensis did not react to
the odors of conspecifics when presented to them on cotton swabs.
2. Though most T. brasiliensis roosted randomly with conspecifics,
some exhibited a tendency to roost preferentially with specific
individuals.
3. Individual T. brasiliensis were able to distinguish familiar from
unfamiliar individuals on the basis of scent alone. The statistical
tests supported the hypothesis that T. brasiliensis are able to
discriminate between unfamiliar and familiar individuals on the basis
of scent, and that they prefer the scent of familiar pouches to
unfamiliar or control pouches.
4.2 Experiment 1 Testing the response of captive bats to the
glandular secretions of conspecifics
In experiment 1, cotton swabs containing the odors of conspecifics were
presented to individuals in a testing arena. Fourteen of the fifteen bats
showed no response directed towards any of the swabs during
experimental trials. Because one male directed obvious investigative
behavior towards a swab on one occasion, and because the odor on the
swabs was detectable by humans, I am confident that the cotton swabs
presented an adequate level of stimulus to which the bats could react.
The most probable explanation for the lack of behavioral response in this
experiment is that it did not provide an appropriate cue to the bats to
elicit a response.
4.3 Experiment 2 Testing whether bats in a small captive colony
show a preference for roosting with specific colony members
The roosting choices of a rehabilitated colony of T. brasiliensis were
recorded for a period of one week to determine whether the bats
exhibited a tendency to roost consistently with specific individuals
within the colony. Although most of the bats roosted randomly with
24


other individuals throughout the week, there were several bats in each
cage which roosted with another specific individual more than chance
would dictate.
All three of the juveniles showed stronger roosting preferences than the
adults. The two juvenile females roosted with each other constantly and
also associated preferentially with one adult. The juvenile male
significantly preferred roosting with two adult males. This result is not
unexpected, because T. brasiliensis is an exceptionally social species,
and bats have demonstrated social transmission of information between
individuals (Page and Ryan 2006). This might be especially important
for first-year juveniles.
To maximize the sample size, I included the geriatric bats in the analysis
despite there being a small number of bats in the cage. Two of the
geriatric bats demonstrated a strong preference to roost with each other,
despite the presence of various other bats in the cage. These two bats
had been in association for a longer time period than many of the other
bats, and demonstrated a stronger roosting preference than any other
adult bats. The idea that bats might form stronger associations with time
is one that merits further study.
Several adult females and adult males showed a roosting preference. As
a whole, more females demonstrated roosting preferences than the males.
During the breeding season, breeding males establish and defend a
territory within a pouch in the roosting cage, and the tendency of males
to roost alone could be an extension of this, though the study did not
overlap with the reproductive period for this species. Also, it has been
suggested that female bats are more temperature-dependent than males,
and generally prefer warmer temperatures (Lewis 1993). There were
heating pads provided in all three of the roosting cages, and female bats
were discovered clumped on the heating pad during more of the
observations than males, perhaps affecting their ability to distribute
themselves throughout the pouches in the cage.
4.4 Experiment 3 Testing whether bats use a system of chemical
recognition of roost mates to choose roost sites
25


Individual T. brasiliensis demonstrated an ability to distinguish familiar
from unfamiliar bats based on chemical cues alone in experiment 3. Bats
chose to enter or burrow under or behind familiar scented pouches more
than unfamiliar or control scented pouches, and rejected unfamiliar
pouches more than familiar pouches in this experiment. Results from the
statistical tests supported the hypothesis that T. brasiliensis are able to
discriminate between unfamiliar and familiar colony odors on the basis
of scent, and that they prefer the scent of familiar pouches to unfamiliar
or control pouches.
Bats refused to enter (rejected) unfamiliar pouches more often than
familiar pouches in this experiment, demonstrating that not only can bats
discriminate between these odors, but also that they make roosting
choices based on them. Although this is a highly gregarious and colonial
species, most of the focal animals refused to roost in a pouch which
contained unfamiliar scents when given a choice including control
pouches and pouches which contained familiar odor. Bats can be
extremely sensitive to disturbance, and may abandon a roost which has
been entered by humans. If some individuals in a colony refuse to roost
in an area which contains the residual scent of conspecifics, and there are
a limited number of appropriate roost sites in the environment, this could
have important implications for conservation as an increasing number of
roosts are disturbed.
Bats entered and burrowed under or behind familiar pouches more often
than either unfamiliar pouches or control pouches throughout the course
of the experiment. It is not surprising that bats prefer to roost in pouches
which contain the odors of familiar individuals, but it is remarkable that
bats have the ability to detect differences in colony scent profiles, despite
the fact that all the bats in both colonies subsist on the same diet, have
similar roosting conditions, and are not related. Because all the
individuals are probably unrelated, there are no mechanisms such as
phenotype matching being employed in this system; the bats are learning
the unique colony scent profile and discriminating based upon it. Each
colony of bats could possess a unique scent profile produced by
glandular secretions, urine, feces, and products of the microbial
community, which could be detected and learned by bats within the
colony.
26


These data are novel because they clearly show that discrimination in T.
brasiliensis can occur on the basis of odor alone in a free-choice study.
Previous studies of this behavior have tested bat behavior in terms of a
binomial choice, and control odors were not used. De Fanis and Jones
(1995) demonstrated the ability of Common Pipistrelles (P. pipistrellis)
to discern between roostmate and non-roostmate odors, but they used a
positive reinforcement training method rather than the observation of
normal behaviors, and tested the bats using the binomial choice of a y-
maze. Additionally, these bats were taken from the same natural
colonies, so the bats are more likely to be related to one another, though
the genetic relationship is not known. This study therefore was not able
to determine whether bats were utilizing a system of kin recognition or
learned roostmate recognition. Bouchard (2001) studied sex and
roostmate recognition in Angolan Free-tailed Bats (M condylurus) and
Little Free-tailed Bats (Chaerephon pumilus), but also designed a study
with an arena which tested a binomial choice using roostmates from a
natural population. Bloss et al. (2002) determined that Big Brown Bats
(E. fuscus) had the ability to distinguish between familiar and unfamiliar
odors, but their study was conducted in a y-maze. None of the studies
cited above involved control odors, or a population of unrelated bats.
This study demonstrates that individual T. brasiliensis preferentially
roost in a pouch containing familiar scent rather than either a clean roost
or a roost with residual odors of unfamiliar bats. Roostmate recognition
might be used as a gauge of the social history of a site, which might be
an indicator of roost quality. Additionally, this study demonstrates that
in T. brasiliensis, roostmate recognition can occur by some mechanism
other than one related to kin selection, such as phenotype matching,
because none of the bats used in the focal group were related.
4.5 Significance of Research
Chemical communication plays a crucial role in the complex
communication of temperate bats, and might have a significant effect on
the manner in which they choose roost sites and maintain stable colonies
at the roosts. An understanding of how bats relate to each other
27


chemically and how this is important in roost choice could prove to be
important in understanding how bats choose roosts on a larger scale in a
natural environment. It is unknown why bats choose the roosts they do
throughout the year, why they tend to have a high site fidelity, why
autumn swarming sites are chosen, and why swarming sites act as a
rendezvous point for bats from many colonies, even in species which
have remarkably stable colonies during the rest of the year. The answer
to some of these questions probably involves the chemical signals readily
recognized by bats within a colony, and an understanding of the basic
mechanisms of chemical communication in bats could help to elucidate
some of the mysteries of roost choice, providing information which
could then be used in conservation management.
1
28


BIBLIOGRAPHY
Adams, R.A. Bats of the Rocky Mountain West: Natural History, Ecology, and
Conservation. Boulder, Colorado: University Press of Colorado, 2004.
Bloss, J. Olfaction and the Use of Chemical Signals in Bats. Acta
Chiropterologica 1.1 (1999): 31-45.
Bloss J., T. E. Acree, J.M. Bloss, W.R. Rood, T.H. Kunz. Potential Use of
Chemical Cues for Colony-Mate Recognition in the Big-Brown Bat,
Eptesicusfuscus Journal of Chemical Ecology 28.4 (2002): 819-834.
Bouchard, S. Sex Discrimination and Roostmate Recognition by Olfactory
Cues in the African Bats, Mops condylurus and Chaerephon pumilus
(Chiroptera: Molossidae). Journal of Zoology 254 (2001): 109-117.
Burland, T.M., E.M. Barratt, M. A. Beaumont, and P.A. Racey. Population
Genetic Structure and Gene Flow in a Gleaning Bat, Plecotus auritus.
Proc. R. Soc. Lond. B. 266.1422 (1999): 975-980.
Crichton, E.G., and P.H. Krutzsch. Reproductive Biology of Bats. Cambridge:
Academic Press, 2000.
De Fanis, E., and G. Jones. The Role of Odour in the Discrimination of
Conspecifics by Pipistrelle Bats. Animal Behavior 49 (1995): 835-839.
Dechmann, D.K.N., and K. Safi. Studying Communication in Bats.
Cognition. Brain. Behavior 9.3 (2005): 479-496.
Gustin, M.K. and G.F. McCracken. Scent Recognition Between Females and
Pups in the Bat Tadarida brasiliensis mexicana. Animal Behavior 35
(1987): 13-19.
Heideman, P.D., K.R. Erikson, and J.B. Bowles. Notes on the Breeding
Biology, Gular Gland, and Roost Habits of Molossus sinaloae
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(Chiroptera, Molossidae). Zeitschrift fur Saugetierkunde 55 (1990): 303-
307.
Kerth, G., F. Mayer, and E. Petit. Extreme Sex-Biased Dispersal in the
Communally Breeding, Nonmigratory Bechsteins Bat (Myotis
bechsteinii)'' Molecular Ecology 11 (2002): 1491-1498.
Kerth, G., F. Mayer, and B. Konig. Mitochondrial DNA (mtDNA) Reveals
that Female Bechsteins Bats Live in Closed Societies. Molecular
Ecology 9 (2000): 793-800.
Lewis, S.E. Effect of Climatic Variation on Reproduction by Pallid Bats
(Antrozous pallidus). Canadian Journal of Zoology 71 (1993): 1429-
1433.
Loughry, W.J. and G.F. McCracken. Factors Influencing Female-Pup Scent
Recognition in Mexican Free-Tailed Bats. Journal of Mammalogy 72.3
(1991): 624-626.
Nielson, L.T., D.K. Eaton, D. W. Wright, and B. Schmidt-French.
Characteristic Odors of Tadarida brasiliensis mexicana (Chiroptera:
Molossidae). Journal of Cave and Karst Studies 68.1 (2006): 27-31.
Page, R.A., and M.J. Ryan. Social Transmission of Novel Foraging Behavior
in Bats: Frog Calls and Their Referents. Current Biology 16 (2006):
1201-1205.
Veith, M., N. Beer, A. Kiefer, J. Johannesen, and A. Seitz. The Role of
Swarming Sites for Maintaining Gene Flow in the Brown Long-Eared Bat
(Plecotus auritus). Heredity 93 (2004): 342-349.
Voigt, C.C. Production and Display of Odor in Courting Male Saccopteryx
bilineata. Bat Research News 40.3 (1998): 104.
Voigt, C.C., and O. von Helverson. Storage and Display of Odour by Male
Saccopteryx bilineata (Chiroptera, Emballonuridae). Behavioral
Ecology and Sociobiology 47 (1999): 29-40.
30


Chapter 2
Observations of Swarming Bats at Groaning Cave, Garfield County,
Colorado


1. Introduction
Many species of temperate bats change geographic location seasonally. In the
fall, approximately twenty-six species of bats within seven genera distributed
worldwide participate in a behavior known as swarming (Parsons et al. 2003b),
during the course of which mating occurs, and winter roosts called hibemacula
are chosen. During the colder months, bats congregate in the hibemacula where
they hibernate until spring. In the spring, bats leave in search of summer roosts,
and fertilization occurs at this time using sperm stored from the previous autumn
(Adams 2004). In the summer, many species exhibit roost segregation behavior:
parous females live together in maternity colonies, while males and
reproductively inactive females live singly or in bachelor colonies (Adams 2004).
For many species, caves are suitable roosts at all of these stages because of the
protection from environmental factors and predators and the consistent physical
environment that they provide.
Generally, swarming behavior involves groups of bats pursuing each other
repeatedly in and out of cave or mine entrances in the period between the
disbanding of maternity colonies and the onset of hibernation (Rivers et al. 2006).
Swarming behavior originally was defined as the behavior of bats surrounding
hibemacula in caves or mines during the late summer and fall (Fenton 1969).
However, in the decades since preliminary observations of swarming behavior, it
has become apparent that not all bats hibernate at swarming sites (Davis and
Hitchcock 1965; Fenton 1969; Fenton and Barclay 1980; Gates and Johnson
2006; Rivers et al. 2006). Swarming generally represents the highest seasonal
activity levels for the sites where it occurs (Cope and Humphrey 1977; Gates and
Johnson 2006; Kunz 1971; Mumford and Whitaker 1975; Parsons et al. 2003a).
This behavior is most often seen in cavernicolous bat species in temperate zones
(Johnson et al. 2006). Species belonging to the cosmopolitan genus Myotis are
especially common at swarming sites (Parsons et al. 2003b; Rivers et al. 2006)
(Table 6). Swarms often consist of many different species (Agosta et al. 2005;
Gates and Johnson 2006; Navo et al. 2002).
At northern-temperate sites, swarming behavior begins as early as mid-July when
males and non-parous females begin to arrive (Fenton and Barclay 1980). Results
from trapping or netting at swarming sites during this time indicate there is a
male-biased sex ratio, with males accounting for the majority of captures in the
beginning of August (Navo et al. 2002). At swarming sites in most areas, there is
32


a peak in swarming activity between the end of August to the middle of
September, depending on climate (Agosta et al. 2005; Bauerova and Zima 1988;
Parsons et al. 2003a; Schowalter 1980). During the peak swarming period, the
ratio of females to males increases as females begin to arrive, and in some cases
the sex ratio approaches 50:50 (Davis and Hitchcock 1965; Fenton and Barclay
1980). As the season progresses, the proportion of females decreases again, while
the number of males generally remains the same (Gates and Johnson 2006; Rivers
et al. 2006).
Recapture rates at swarming sites are very low, suggesting that there is a high
level of turnover from night to night, and that bats might be visiting more than
one swarming site (Gates and Johnson 2006; Johnson et al. 2006). Recapture
rates from year to year range from only a few bats to as high as 80%, suggesting
that the level of seasonal site fidelity might differ among species and swarming
sites (Navo et al. 2002; Tinkle and Patterson 1965).
Activity levels differ from night to night over the swarming season, but some
general patterns among nights exist (Navo et al. 2002; Parsons et al. 2003b). If
bats are day-roosting in a cave or mine, there is an emergence peak beginning at
sunset, then swarming activity peaks again later in the night (Rivers et al. 2006),
though most researchers report that bats do not generally day-roost at swarming
sites (Cope and Humphrey 1977; Parsons et al. 2003a). If bats are not day-
roosting in the cave or mine, activity begins at low levels, then peaks anywhere
from 3-7 hours after sunset as bats arrive from other sites, presumably after
foraging (Agosta et al. 2005; Bauerova and Zima 1988; Davis and Hitchcock
1965; Parsons et al. 2003b; Rivers et al. 2006). Bats arriving from elsewhere
often circle the cave mouth before entering and exiting repeatedly during the
course of the night (Rivers et al. 2006). Radio-tracking studies in North America
have shown that bats can day-roost in adjacent habitat, or up to 27 km away from
the swarming site (Rivers et al. 2006).
Physical site factors influence swarming behavior. Johnson et al. (2006)
demonstrated that external characteristics of mines were correlated with bat use
during swarms. Internal characteristics are also important. Hibemacula are
chosen in the coldest portions of caves with the lowest average temperature in one
study (Clark et al. 1996), possibly because basal temperatures of bats during
torpor is mostly determined by the temperature of the roosting substrate. If the
substrate is colder, the average temperature of the bat is lower, and thus the bat
33


has a higher chance of overwintering without catabolizing too many of its fat
reserves (Clark et al. 1996). If some swarming sites are used as hibemacula, this
might help explain why high-elevation caves with lower temperatures might be
chosen as swarming sites.
Abiotic environmental variables influence swarming behavior, though there is a
large disparity in published reports. Several researchers have found a correlation
between swarming activity and temperature (Parsons et al. 2006b; Whitaker and
Rissler 1992), and several have not (Agosta et al. 2005; Brack 2006). In some
cases, there is a positive relationship between temperature and bat activity
(Parsons et al. 2003a; Whitaker and Rissler 1992), perhaps attributable to the fact
that temperature affects distribution and activity levels of insects. Bats at higher
latitudes have longer gestation periods, a fact attributed to a lower average
temperature (Reeder et al. 2004), and bats in maternity colonies during cold years
have longer gestation periods and are less likely to mate the next year (Lewis
1993), facts which also could influence the number of receptive females at
swarming sites (Lewis 1993). Several researchers have found that temperature
might not have a direct effect on swarming activity until a threshold is reached,
below which there is little activity. Threshold values are reported to be 10-12 C
(Agosta et al. 2005), 13 C (Parsons et al. 2003a), and -8 C (Schowalter 1980).
Parsons et al. (2003a) suggested that temperature is most important for swarming
bats in determining emergence times, and thus would be a more important
variable seasonally than nightly.
Duration of bat activity each night generally is correlated with night length
because there is a strong correlation between bat activity and large changes in
light intensity (Erkert 1978). Brightness of moonlight does not seem to affect the
activity level of temperate bats during swarming (Karlsson et al. 2002; Parsons et
al. 2003a), although some species fly higher on moonlit nights when foraging or
spend more time foraging in shadows (Hecker and Brigham 1999; Reith 1982).
Karlsson et al. (2002) suggested that temperate bats fly in bright moonlight during
swarming because the possible benefits of a larger number of matings exceeds the
perceived risk of predation.
Atmospheric pressure might correlate to bat activity at swarming sites for several
reasons. Fluctuations in atmospheric pressure can signal impending storms, and
high steady pressures can indicate clear weather. Changes in atmospheric
pressure can change patterns of airflow within cave mouths, a phenomenon called
34


cave breathing, which could then affect bat activity within the cave mouth
(Lewis 1991).
In contrast to the severe impact of rain on bat activity in normal circumstances
(Grindal et al. 1992), several researchers have shown that rain has little effect on
swarming bats (Navo et al. 2002). In contrast, Parsons et al. (2003a) reported a
negative correlation between swarming activity rates and rainfall, and suggested
that rainfall would have a greater effect on swarming activity if it began before
bats departed day roosts for swarming sites.
The ultimate explanation for swarming behavior in bats is poorly understood.
There are several hypotheses to explain the commonality of this behavior in
temperate bats. Swarming behavior generally is held to be important in mating
behavior and gene flow, but it also has been suggested that swarming serves in the
selection of hibemacula, and/or allows the social transmission of foraging or
mating information to juveniles (Davis and Hitchcock 1965; Fenton 1969;
Johnson et al. 2006; Rivers et al. 2006).
There have been a number of researchers who have presented data suggesting that
swarming behavior plays a vital role in the reproduction of temperate bat species.
Several researchers reported observing bats mating on the walls of caves or mines
used as swarming sites (Bauerova and Zima 1988; Parsons et al. 2003b; Rivers et
al. 2005; Senior et al. 2005). The swarming season corresponds with the peak of
the mating season for many species (Rivers et al. 2005), and also the peak in
reproductive condition of males and receptivity of females (Gustafson and
Shemesh 1976; Rivers et al. 2005). In some species, however, mating is not
limited to the swarming season, and mating occurs in both maternity colonies and
hibemacula (Fenton and Barclay 1980; Rivers et al. 2005).
Female temperate bats are often highly philopatric, returning to their natal roost to
bear young (Kerth et al. 2002a; Petit and Mayer 2000; Rivers et al. 2006), and so
many colonies have members which are related along matrilines (Kerth et al.
2002b; Rivers et al. 2005). There is a very low level of roost-switching in some
swarming species, despite the close proximity of other colonies (Rivers et al.
2006).
In most species of swarming bats, males are the dispersing sex (Kerth et al.
2002b), but in some species, males are philopatric as well as females (Burland et
35


al. 1999; Rivers et al. 2005). Philopatry can be beneficial in populations because
it creates conditions where roosts can be used from year to year, and behaviors
such as kin selection, helping behaviors, predator defense, clumping for
thermoregulation, and grooming can be fostered (Rivers et al. 2005). The
disadvantage to strict philopatry is the loss of genetic variability over time due to
inbreeding. Despite strict philopatry in many swarming species, there is a high
genetic variability among colonies tested, suggesting that there must be some
mechanism for gene flow to occur (Kerth et al. 2003). Swarming sites include
bats from several different colonies, which would allow gene flow to occur (Veith
et al. 2004). Several researchers have shown that there is a higher level of genetic
diversity at swarming sites than at maternity colonies, especially when analyzing
mitochondrial DNA (Petit and Mayer 2000; Veith et al. 2004). The level of
genetic diversity as measured by heterozygosity has been shown to be vital to
survivorship in several species of temperate bats (Rossiter et al. 2001). The
mixing of colonies during swarming behavior might provide a mechanism by
which the low reproductive skew and high measured levels of genetic diversity in
temperate bat populations can be achieved (Burland et al. 1999; Kerth et al. 2002;
Rivers et al. 2005; Rossiter et al. 2001), and in fact the genetic diversity of some
species of temperate bats can be explained sufficiently by swarming behavior
alone (Rivers et al. 2005).
Often there is a male-biased sex ratio at swarming sites (Gates and Johnson 2006).
Males typically represent 80-96% of captures during swarming (Navo et al. 2002;
Senior et al. 2005), though during the peak of activity the percentage of males to
females can drop to as low as 50% (Cope and Humphrey 1977). At some sites,
there is a male-biased sex ratio during autumn, but a 1:1 ratio of males to females
upon emergence from hibemacula (Rivers et al. 2006). The species which exhibit
swarming behavior are all promiscuous species which typically only bear one pup
per year. Because the ratio of males to females in the general population is
reported to be roughly equal, there is probably intense competition for mates
among males.
If swarming sites provide a rendezvous point for bats from many colonies, they
also provide mating opportunities. Because they only bear one young, females
theoretically can benefit most from mating once with a good-quality male (which
they can choose from the group of males present at the swarming site) and then
concentrating on building up fat reserves and entering hibemacula early. Males,
on the other hand, will benefit most from multiple matings and might stay at the
36


swarming site longer to mate with females that arrive later (Rivers et al. 2006;
Senior et al. 2005). In fact, males tend to arrive at the swarming site early, and
enter hibemacula later than females (Gates and Johnson 2006). Females might
arrive at swarming sites when the males are in maximum reproductive condition,
mating once, and then leaving, creating the fluctuating ratio of females to males
described above (Rivers et al. 2006). This suggestion is supported by the fact that
recaptures at swarming sites during a season often are 100% male (Navo et al.
2002; Parsons et al. 2003a).
There is a much smaller body of evidence which supports the hypothesis that
swarming behavior serves as an assessment of potential hibemacula or for social
learning. Veith et al. (2004) found that in some species there are small numbers
of females successfully impregnated at swarming sites, suggesting that swarms
might have another function beyond mating and gene flow. Additionally, Fenton
(1969) indicated that the ratio of juveniles to adults at swarming sites was
approximately 1:1, suggesting that some swarming sites might be particularly
important to bats during their first year.
Swarming behavior has been described most extensively in the United Kingdom
and the eastern United States, and very little information is available for the
western United States (Navo et al. 2002). Swarming behavior is little understood,
but whatever its purpose, it is almost certainly vital to the life cycle of many
temperate bats. There is strong evidence that swarming behavior is important in
mating behavior and gene flow, but it also might serve other social functions. If
swarming sites are important for the maintenance of high levels of genetic
variability in swarming populations, they merit both regular monitoring and
protection if necessary, especially if they are used by threatened species. The aim
of this project, documenting the basic activity patterns of a swarm at Groaning
Cave and correlating these patterns with environmental variables, will provide
important information about swarming in Colorado. Based on swarming studies
in other areas (Agosta et al. 2005; Bauerova and Zima 1988; Brack 2006; Cope
and Humphrey 1977; Fenton 1969; Gates and Johnson 2006; Karlsson et al. 2002;
Kunz 1971; Lewis 1991; Lewis 1993; Mumford et al. 1975; Navo et al. 2002;
Parsons et al. 2003a and b; and Rivers et al. 2006), I hypothesized that swarming
behavior will peak 4-7 hours after sunset each night and seasonally in mid-
September. Based on a review of the literature detailed above, if correlations with
abiotic factors are present, bat activity are hypothesized to be positively correlated
37


with temperature, air pressure, and cloud cover, and negatively correlated with
humidity, wind speed, light intensity, and moon brightness.
I tested the following hypotheses in this study:
1) Activity of swarming bats at Groaning Cave will show patterns similar to
those at sites in the eastern United States and Great Britain: There will be
a nightly activity peak 4-7 hours after sunset, and a seasonal activity peak
in mid-September.
2) Activity of swarming bats at Groaning Cave will be correlated positively
with temperature, air pressure, and cloud cover.
3) Activity of swarming bats at Groaning Cave will be negatively correlated
with humidity, wind speed, light intensity, and moon brightness.
38


Table 6: Table of species documented at the swarm at Groaning Cave. Source:
Navo et al. 2002. Data were collected during the autumn swarming season in
1981, 1982, 1993, 19977, 1999, 2001, and 2004. This table demonstrates the high
species diversity at the Groaning Cave swarm.
Species Common Name
Eptesicus fuscus Big brown bat
Myotis bechsteinii Bechsteins bat
Myotis ciliolabrum Western small-footed myotis
Myotis daubentoni Daubentons bat
Myotis evotis Long-eared myotis
Myotis leibii Small-footed myotis
Myotis lucifugus Little brown myotis
Myotis myotis Greater mouse-eared bat
Myotis nattereri Natterers bat
Myotis septentrional is Northern myotis
Myotis sodalis Indiana bat
Myotis volans Long-legged myotis
Myotis yumanensis Yuma myotis
Nyctalus noctula Noctule bat
Pipistrellus subflavus Eastern pipistrelle
39


2. Methods
2.1 Research Models and Study Location
Swarming studies were completed on seven nights between August 30,2007 and
October 5, 2007 at the mouth of Groaning Cave in Garfield County, Colorado
(Figure 7), a known autumn swarming site (Navo 2002). The cave is located in a
limestone gorge 24 kilometers long and 1.5 kilometers wide at approximately
2988 meters in elevation, and the surrounding vegetation is mostly comprised of
Douglas Fir and Aspen trees. The study site was suggested by Kirk Navo of the
Colorado Division of Wildlife, and the research was authorized by the area
National Forest Service office. The most common species at the site all belong to
the genus Myotis, the mouse-eared bats (Navo 2002).
2.2 Experiment 1: Cataloging the general activity patterns of autumn
swarming behavior
This experiment was designed to test the hypothesis that the activity of bats
during the autumn swarm shows variability throughout each night and the course
of the swarming season. Bat activity at the cave entrance was monitored
overnight for seven nights roughly once per week between August 30, 2007 and
October 5, 2007. All times reported in the study reflect Mountain Standard
Daylight Saving Time.
A Sony Nightshot DCR-SR62 camera was set up immediately inside the cave
mouth entrance, facing down into the cave. Two IRLamp6 (Wildlife
Engineering) infrared lights were set up on a light bar on either side of the
camera. The IRLamp6 has an average luminous intensity of 810 nanometers, an
average radiant intensity of 6120 mW/sr, and an illuminated angle of 20 degrees.
The battery life of the camera exceeded eight hours, while the two 12-volt
batteries for the IRLamp6 generally have a battery life of eight to ten hours. The
wavelength of the infrared beam emitted by the light has been designed by
Wildlife Engineering to be short enough to be picked up on video cameras with
infrared sensors, but long enough to avoid disturbing nocturnal wildlife. A Hobo
H8 data logger (Onset Computer Corporation) was used at the site to monitor
temperature, humidity, and light intensity at two minute intervals.
40


Experimental set up was completed before dusk to minimize disturbance. The
video camera and infrared lights were attached to a light bar on a tripod which
was placed at the entrance of the cave mouth, and the data logger was placed on a
flat rock inside the cave mouth. One other trained observer and I sat just outside
the cave entrance and recorded the time when the first bat was spotted, and when
the first bat entered the cave. About an hour after dark, the camera and infrared
lights were turned on, and were allowed to run until the batteries ran out (8-10
hours).
I analyzed each video in two ways: 1) by counting the number of bats present in
one frame every two minutes, and 2) by measuring the rate of bat activity, the
number of bats entering or exiting the cave entrance in a five minute duration
measured every twenty minutes of time. First, the number of bats per frame at
two-minute intervals synchronized to the Hobo data logger readings was
recorded. Next, to measure rate of bat activity, two cell counters were used to
determine the number of bats flying in and out of the entrance during five minute
intervals. Because swarming behavior generally entails rapid flight in and out of
the cave mouth and because of the difficulty of identifying individual bats, an
absolute scale was used; any movement into the cave mouth was considered in
and any movement out of the cave mouth was considered out, regardless of
length of the flight path. Rate of bats was calculated by dividing the number of
bats which had flown in or out of the cave mouth by the 5 minute time period.
We are making the tacit assumption that there is an independence of data in these
measurements. There is no way to determine this from our analysis, however,
previous data sets from this site (Navo et al. 2002) demonstrate very low
recapture rates over the course of each night.
2.3 Experiment 2: Testing whether abiotic environmental factors affect
swarming behavior
This observational study was designed to test the hypothesis the changes in
autumn swarming activity of Coloradan bats can be correlated to environmental
variables. General environmental data, including moon phase, sunset, wind
speed, cloud cover, and precipitation information were obtained from the Eagle
Airport (Eagle, Colorado, U.S.A.) for each night of the study. Abiotic
environmental data specific to the site, such as local temperature, humidity, and
light intensity were recorded every two minutes at the cave mouth with an H8
Hobo data logger (Onset Computer Corporation). Environmental data were then
41


correlated with the activity levels and rates calculated throughout the season in
experiment 1 using simple linear regression with two-tailed P values.
42


43


3.
Results
3.1 Nightly Patterns
Bats in the Groaning Cave swarm exhibited activity patterns throughout the
course of each night, and the season as a whole, which were consistent with
patterns reported for swarms in other regions (Agosta et al. 2005; Bauerova and
Zima 1988; Brack 2006; Cope and Humphrey 1977; Fenton 1969; Gates and
Johnson 2006; Karlsson et al. 2002; Kunz 1971; Lewis 1993; Mumford et al.
1975; Navo et al. 2002; Parsons et al. 2003 a and b; and Rivers et al. 2006).
Activity rate was calculated from the number of bats entering and the number of
bats exiting the cave mouth for five minute time periods. Activity level was
measured as the number of bats per frame of video at two minute intervals.
Activity rate peaked on average 3 hours and 43 minutes after sunset, and activity
level peaked on average 4 hours and 21 minutes after sunset. Activity rate and
level slowly decreased until sunrise after peaking (Figures 8, 9, and 10).
August 30, 2007 was the first day of the survey. The first recorded activity rate
was low (5.4 bats per minute, 23.28% of the maximum activity rate). Maximum
activity rate was observed at 23:45:00 (Figure 8) and maximum activity level at
23:46:00 (Figure 9). The maximum activity rate and level were observed 4 hours
and 3 minutes and 4 hours and 4 minutes after sunset, respectively (Table 7). On
this date, bat activity rates were correlated positively with cave temperature
(linear regression, P = 0.0429). Bat activity levels were positively correlated with
cave temperature on this date (linear regression, P = 0.0258).
On September 2,2007, activity rates and levels were low (1.8 bats per minute,
10.34% of the maximum activity rate) at the beginning of the night. Maximum
activity rate occurred at 0:00:00 (Figure 8) and maximum activity level occurred
at 0:24:00 (Figure 9). The maximum activity rate occurred 4 hours and 23
minutes after sunset, and the maximum activity level occurred 4 hours and 47
minutes after sunset (Table 7). On this date, bat activity rates were positively
correlated with cave temperature (linear regression, P = 0.0005) outside
temperature (linear regression, P = 0.0104), and air pressure (linear regression, P
= 0.0087) and negatively correlated with cave relative humidity (linear regression,
P < 0.0001) and outside relative humidity (linear regression, P = 0.0251). Bat
activity levels were positively correlated with cave temperature (linear regression,
I
44


P = 0.0008) and negatively correlated with cave relative humidity (linear
regression, P < 0.0001).
On September 10, 2007, activity rates and levels started at a higher level (6.6 bats
per minute, 78.5% of the maximum activity rate) than the previous two nights.
Maximum activity rate occurred at 23:45:00 (Figure 8), and maximum activity
levels occurred at 22:51:00 (Figure 9). The maximum activity rate occurred 4
hours and 21 minutes after sunset. The maximum activity level occurred 3 hours
and 27 minutes after sunset (Table 7). On this date, bat activity rates were
positively correlated with cave temperature (linear regression, P < 0.0001),
outside temperature (linear regression, P = 0.0003), and air pressure (linear
regression, P 0.0005). Bat activity rates were negatively correlated with cave
relative humidity (linear regression, P 0.0002), outside relative humidity (linear
regression, P = 0.0009), and wind speed (linear regression, P = 0.0012) on this
date. Bat activity levels were positively correlated with cave temperature on this
date (linear regression, P 0.0038).
On September 14, 2007, activity rates and levels were low (2.6 bats per minute,
19.69% of the maximum activity rate) at the beginning of the night. Maximum
activity rate occurred at 23:30:00 (Figure 8), and maximum activity levels were
first observed at 23:46:00 (Figure 10). The maximum activity rate occurred 4
hours and 12 minutes after sunset, and maximum activity levels occurred 4 hours
and 28 minutes after sunset (Table 7). On this date, bat activity rates were
positively correlated with cave temperature (linear regression, P = 0.0248). Bat
activity levels were not correlated with any environmental variables on this date.
On September 21, 2007, activity rates and levels started at a fairly high level (10.8
bats per minute, 66.67% of the maximum rate). At approximately 23:10:00 on
this date, the camera was turned towards the wall by a Bushy-tailed Wood Rat
(.Neotoma cinerea) which was denning in the cave mouth. Therefore, September
21, 2007 represents only a partial night of data. Maximum activity rate occurred
at 20:45:00 (Figure 8), and maximum activity level occurred at 20:30:00 (Figure
10). Maximum activity rate occurred 1 hour and 39 minutes after sunset, and
maximum activity level occurred 1 hours and 24 minutes after sunset. Because
this night represents only a partial night of data, however, it is likely that there
was also a peak in activity 3 hours later after the camera had been turned away
from the cave mouth, and consistent with the rate and level peaks on other nights
(Table 7). On this date, activity rate was positively correlated with cave
45


temperature (linear regression, P = 0.0241) and negatively correlated with wind
speed (linear regression, P = 0.0116). Bat activity levels were positively
correlated with cave temperature on this date (linear regression, P = 0.0074).
On September 28,2007, activity rates started at a high level (3.8 bats per minute,
100% of the maximum rate) in comparison to the rest of the nights activity but a
fairly low level overall. Maximum activity rate occurred at 21:00:00 (Figure 8)
and maximum activity level occurred at 23:39:00 (Figure 10). The maximum
activity rate was observed 2 hours and 5 minutes after sunset, though there were
several smaller rate peaks later in the night that were more consistent with the rate
peaks of other nights at 22:30:00 and 0:00:00 (Table 7). The maximum activity
level occurred 4 hours and 44 minutes after sunset. On this date, activity rate was
positively correlated with cave temperature (linear regression, P = 0.0228) and
negatively correlated with cave relative humidity (linear regression, P = 0.0265).
Bat activity levels were not correlated with any environmental variables on this
date.
On October 5, 2007, activity rates and activity levels started at a low level (0.4
bats per minute, 100% of the maximum rate) and remained low throughout the
night. The maximum activity rate occurred at 22:00:00 (Figure 8), and the
maximum activity level occurred at 23:20:00 (Figure 10). The maximum activity
rate occurred 3 hours and 16 minutes after sunset, and the maximum activity level
occurred 4 hours and 36 minutes after sunset (Table 7). On this date, there were
no variables that were significantly correlated with activity rates, partially because
by this date, the activity levels were almost zero. Bat activity levels were not
correlated with any environmental variables on this date.
3.2 Seasonal Patterns
Activity rates and levels showed a pattern throughout the course of the swarming
season which is consistent with the observations of swarms in other regions
(Agosta et al. 2005; Bauerova and Zima 1988; Brack 2006; Cope and Humphrey
1977; Fenton 1969; Gates and Johnson 2006; Karlsson et al. 2002; Kunz 1971;
Mumford et al. 1975; Navo et al. 2002; Parsons et al. 2003 a and b; and Rivers et
al. 2006). Because only a partial night of data was collected on September 21,
2007, and because this night represented one of the highest activity rates and
levels throughout the season, all of the seasonal activity was calculated from the
time range on each night which was captured on September 21, 2007. All rates
46


given represent the mean of nightly data. The rate began fairly high (5.49 bats per
minute) on August 30, 2007, suggesting that the swarming season had already
begun at the end of August. Activity rate peaked on September 2,2007 (8.3 bats
per minute), and on September 21, 2007 (7.98 bats per minute). After the second
peak occurred, activity rate sharply decreased, and significant activity rates were
absent (.0625 bats per minute) by October 5, 2007, the final study night (Figure
3.4). Activity levels demonstrated roughly the same pattern, but peaked on
September 10, 2007 (average 0.2698 bats per frame), and on September 21, 2007
(average 0.2410 bats per frame) (Figure 11).
All values for individual nights were combined to assess seasonal activity values.
According to regression analysis, seasonal swarming activity rate was positively
correlated with cave temperature (linear regression, P < 0.0001) (Figure 12),
outside temperature (linear regression, P 0.0001) (Figure 13), and air pressure
(linear regression, P = 0.0178) (Figure 16). Seasonal swarming activity rate was
negatively correlated with cave relative humidity (linear regression, P = 0.0005)
(Figure 14) and outside relative humidity (linear regression, P = 0.0014) (Figure
15). Seasonal swarming activity level was positively correlated with cave
temperature (linear regression, P < 0.0001 ) (Figure 17), and negatively correlated
with cave relative humidity (linear regression, P = 0.0159) (Figure 18).
47


a.
b.
c.
Figure 8: Swarming Study Activity Rate. Activity rate (bats entering/exiting the
cave mouth per minute) for each night of the swarming study, August 30, 2007
through October 5, 2007. Each graph reprersents 2-3 nights of data. a. 8/30/07
and 9/2/07. b. 9/10/07 and 9/14/07. c. 9/21/07, 9/28/07, and 10/5/07. Activity
rate generally began at a low level, peaked on average 3 hours and 43 minutes
after civil twilight, then tapered off until sunrise.
48


a.
b.
c.
45 i
0 I........j..II.,..............
888888888888888888888888888
8i55!!!i8SSrS8!J5li8 J?SS85Si88S
Figure 9: Swarming Study Activity Level 1. Activity level (Bats per frame) on a.
August 30, 2007. b. September 2, 2007. c. September 10, 2007. Activity level
generally began at a low level, peaked 4 hours and 21 minutes after civil twilight
on average, then tapered off until sunrise.
49


a.
45
i
0.5 j
0 i
d.
Figure 10: Swarming Study Activity Level 2. Activity level (bats per frame) on a.
September 14, 2007. b. September 21,2007. c. September 28,2007. d. October 5,
2007. Activity level generally began at a low level, peaked 4 hours and 21
minutes after civil twilight on average, then tapered off until sunrise.
50


a.
b.
Figure 11: Seasonal Activity Rate and Level, a. Average seasonal activity rate
(bats per minute) from August 30,2007 to October 5,2007. b. Average activity
level (bats per frame) from August 30, 2007 to October 5, 2007. Activity rate
began at a moderate level on August 30, peaked on September 2, and September
21, then dropped sharply. Significant swarming activity had ceased by October 5,
2007.
51
1


Plot of Fitted Model
Cave Temperature
Figure 12: Seasonal Activity Rate (Bats Per Minute) and Cave Temperature
(Celsius). Linear regression with line of best fit and 95% and 75% confidence
intervals plotted. Seasonal activity rate was significantly correlated with seasonal
cave temperature.
52


Plot of Fitted Model
Figure 13: Seasonal activity rate (bats per minute) and outside temperature
(Celsius). Linear regression with line of best fit and 95% and 75% confidence
intervals plotted. Seasonal activity rate was significantly correlated with seasonal
outside temperature.
53


Plot of Fitted Model
Figure 14: Seasonal activity rate (bats per minute) and cave relative humidity
(%). Linear regression with line of best fit and 95% and 75% confidence intervals
plotted. Seasonal activity rate was significantly correlated with seasonal cave
relative humidity.
54


Plot of Fitted Model
Outside Relative Humidity
Figure 15: Seasonal activity rate (bats per minute) and outside relative humidity
(%). Linear regression with line of best fit and 95% and 75% confidence intervals
plotted. Seasonal activity rate was significantly correlated with seasonal outside
relative humidity.
55


Plot of Fitted Model
Pressure
Figure 16: Seasonal activity rate (bats per minute) and air pressure (mmHg).
Linear regression with line of best fit and 95% and 75% confidence intervals
plotted. Seasonal activity rate was significantly correlated with seasonal air
pressure.
56


Plot of Fitted Model
4
>* 2
>
O 1
<
0
6 8 10 12 14 16 18
Cave Temperature
Figure 17: Seasonal activity level (bats per frame) and cave temperature
(Celsius). Linear regression with line of best fit and 95% and 75% confidence
intervals plotted. Seasonal activity level was significantly correlated with
seasonal cave temperature.
57


Plot of Fitted Model
24 34 44 54 64 74
Cave Relative Humidity
Figure 18: Seasonal activity level (bats per frame) and cave relative humidity
(Celsius). Linear regression with line of best fit and 95% and 75% confidence
intervals plotted. Seasonal activity level was significantly correlated with
seasonal cave relative humidity.
58


Table 7: Summary table of cave data by night.
Date Moon Phase (% Illuminated) Sunset (Time) Sunrise (Time) Average Temp. (Celsius) Average Relative Humidity (%) Average Light Intensity (lum/sqm) Average Wind Speed (kph) Average Cloud Cover Average Precipitation Maximum Activity Rate Time Maximum Activity Level Time
8/30/07 93% 1942 0634 15.4 50.3 21.52 4.18 11.88 0 2345 2346
9/2/07 65% 1937 0637 14.33 55.44 21.52 2.50 19.44 0 000 024
9/10/07 1% 1924 0644 6.78 49.56 10.76 5.01 0 0 2345 2251
9/14/07 9% 1918 0648 14.71 59.43 10.76 9.93 77.68 0 2330 2346
9/21/07 70% 1906 0655 12.33 49 10.76 3.22 0 0 2045 2030
9/28/07 94% 1855 0701 10 63.25 10.76 6.03 51.56 0 2100 2339
10/5/07 26% 1844 0708 11.5 53 10.76 1.21 67.19 0 2200 2320


4.
Discussion
4.1 Summary
1. Swarming bats at Groaning Cave exhibited changes in activity patterns
over the course of the night and the season which were consistent with
values recorded at swarming sites in other areas.
2. Nightly bat activity rate peaked on average 3 hours and 43 minutes
after sunset, and nightly bat activity level peaked on average 4 hours
and 21 minutes after sunset.
3. Low levels of activity at the beginning of the night suggest that it is
not likely that bats are day-roosting at this site.
4. Seasonal swarming activity as measured by number of bats and bat
activity rate at the cave entrance began prior to August 30,2007,
peaked on September 21,2007, and significant activity was absent by
October 5, 2007.
5. Nightly activity was correlated most often with cave temperature, but
on several nights also was correlated with outside temperature, cave
relative humidity, outside relative humidity, wind speed, air pressure,
and cloud cover.
6. Seasonal activity was correlated most strongly with cave temperature
and cave relative humidity, but also was correlated with outside
temperature, outside relative humidity, and air pressure.
Swarming is a unique and poorly understood behavior of some temperate
bats. There is an especially pronounced lack of data regarding this
behavior in the western United States, despite its commonness in the bat
populations which reside there. An understanding of swarming behavior
is vital to the management of bat populations in temperate areas, many of
which are currently threatened by habitat degradation on a vast scale, a
trend also observed in the Colorado environment. Documenting basic
observations at known swarming sites is the first step in building a useful
body on knowledge in this area.
3.1 Nightly Patterns
The bats in the Groaning Cave swarm exhibited predictable patterns
throughout the course of the night which were consistent with those
60


recorded at better studied swarms in the eastern United States and Great
Britain. The hypothesis that swarming activity would peak 4-7 hours after
sunset was supported. On nearly every night of the study, activity rate and
activity level began at a low level which increased to a peak then subsided
again before daybreak. The peak of activity rate and level were fairly
consistent throughout the season, and peaked 3 hours and 43 minutes and
4 hours and 21 minutes after sunset, respectively. The low level of
activity followed by a peak several hours later indicates that bats are
probably not day roosting at this site, a conclusion consistent with most of
the swarming literature. Bats day roosting at other sites were probably
emerging around sunset and foraging before traveling to the swarming site
and creating the peak activity rate.
4.3 Seasonal Patterns
The swarming season had already begun on the first night of the study, so
it is impossible to assign a date to the beginning of swarming activity at
this site. Activity levels were moderate on August 30,2007 on the first
study night. However, I am confident that I accurately recorded the end of
major swarming activity in this study, which occurred between September
28, 2007 and October 5, 2007. Seasonal activity of this swarm was
moderate on August 30, 2007 and peaked on September 2, 2007 and
September 21,2007. After September 21,2007, activity sharply declined.
At this time of the season, heavy snowfall had occurred on at least two
nights, and temperatures were dropping below levels generally tolerated
by active bats. The hypothesis that swarming activity would peak in early
or mid-September was therefore supported.
The hypothesis that temperature would be positively correlated with
swarming activity was supported. Of all the environmental variables
examined in this study, the most commonly correlated with bat activity at
the swarming site was temperature. Cave temperature was correlated with
activity rate on six of the seven nights, and activity level on four of the
seven nights. Outside temperature was correlated with activity rate on two
of the seven nights. Cave temperature was correlated with seasonal
activity rate and seasonal activity level, and outside temperature was
correlated with seasonal activity rate. In all cases, bat activity was
positively correlated with temperature. These data demonstrate that
61


temperature, especially temperature within the cave, might affect bat
behavior. Interestingly, the activity peak on September 21, 2007 was also
an uncharacteristically warm night.
Bat behavior could be correlated with temperature for several reasons. On
warmer nights, there are generally more abundant flying insects (Agosta et
al. 2005). If bats are able to forage enough to balance their energy budget
for the night earlier on warmer nights, they could arrive at swarming sites
earlier and be more active upon arrival. Additionally, thermoregulation is
less costly on warmer nights, perhaps lessening the amount of time bats
need to spend feeding. On the other hand, temperature might correlate
with bat behavior throughout the season merely because temperature and
activity both generally go down as the season progresses and bats prepare
to enter hibemacula. Because bats are endothermic and homethermic
organisms, and because they are small and have a large surface area to
volume ratio, external temperature changes can have a significant effect
on them. In many cases, active bats are cued to enter torpor in low
temperatures, even if the seasonal timing is not correct, illustrating the
intolerance of some species to temperature changes (Bouchard 2001).
The hypothesis that swarming activity would be correlated negatively with
humidity was supported. Relative humidity was correlated negatively
with bat activity on many nights. Relative humidity within the cave was
correlated with bat activity rate on three of the seven nights, and bat
activity level on one of the seven nights. Relative humidity outside of the
cave was correlated with bat activity rate on two of the seven nights.
Seasonal activity rate was correlated with both cave relative humidity and
outside relative humidity, and seasonal activity level was correlated with
cave relative humidity. In all cases, relative humidity was negatively
correlated with bat activity. On at least one of the nights in which activity
was correlated with relative humidity outside of the cave a small rainstorm
occurred. Bats generally avoid flying in the rain, and this could have
reduced their activity. However, there was a substantial lightning storm
which occurred on September 14, 2007 and both cave and outside relative
humidity were not correlated with activity on this date. In fact, activity
levels and rates did not decrease during the storm when compared with
activity before the storm began. Though surprising, this observation also
has been made by Kirk Navo (Navo et al. 2002) at the same site.
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Surprisingly, wind speed was not strongly correlated with bat activity in
this study, and therefore the hypothesis that wind speed would be
negatively correlated with swarming activity was rejected. Wind speed
was correlated with bat activity rate on two of the seven nights, but was
never correlated with activity level, seasonal activity rate, or seasonal
activity level. The average wind speed on the two nights in which wind
speed was correlated with activity were not high when compared with
other nights in the study. This, combined with the fact that on one night
wind speed was positively correlated with activity and on the other it was
negatively correlated suggest that this correlation either occurred due to
chance on the nights in question, or that wind speed is correlated with
another environmental variable which is more important in influencing bat
activity rates.
Air pressure was positively correlated with bat activity in several
instances, and therefore the hypothesis that swarming activity would be
positively correlated with air pressure was supported. Pressure was
correlated with bat activity rates on two of the seven study nights, and
seasonal bat activity rate. Changes in air pressure can be indicative of
changes in general weather patterns which could influence bat activity.
High air pressure generally indicates favorable weather, while lower
pressure can indicate impending rain or windy conditions, which could
lower activity by preventing bats day roosting elsewhere from reaching the
swarming site, or by lowering activity outside of the cave mouth. Also, air
pressure can affect the airflow within the cave mouth, a phenomenon
called cave breathing. It is unknown how changes in cave airflow could
affect swarming activity. Bats might either be sensing changes in pressure
itself, or simply reacting to the weather patterns which are correlated with
pressure differences.
Several other variables measured were not significantly correlated with bat
activity. Bat activity was not correlated on any night or seasonally with
light intensity, moon phase, cloud cover, or visibility, and there was no
quantitative data on precipitation. Therefore, the hypotheses that
swarming activity would be positively correlated with cloud cover, and
negatively correlated with light intensity and moon phase were rejected.
Several previous studies have shown that bat activity is not affected by
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even bright moonlight in temperate areas, and thus moonlight and light
intensity were not expected to have an appreciable effect. Unless the level
of cloud cover affected the precipitation rates, it probably would not have
an appreciable affect either, as it might only change light intensity, which
does not seem to be an important variable.
4.4 Significance of Research
Bats are a vital and misunderstood component of the ecosystems in
Colorado and the West. Effective management of bat populations in the
state hinges on implementing conservation strategies based on life history
information. For many species of bats, this information is missing, and we
are unable to protect or manage many populations.
Though swarming behavior still is not documented or understood fully,
there is an increasing interest in its study to determine the extent of its
occurrence in microchiropterans, and its ultimate purpose in their
populations. If indeed swarming behavior is important in gene flow, it is
imperative that swarming sites are protected during the swarming season.
If swarming sites are destroyed, already threatened and depressed bat
populations might have an increased risk of inbreeding depression due to
low genetic diversity, or fall prey to common problems in small
populations like genetic drift or chance extinction due to stochastic
factors. Even if swarming behavior is only important in the selection of
hibemacula or social learning, it is still an important part of their life
history, without which the populations might suffer.
A record of the basic natural history information of the bat populations in
Colorado, including important roosting sites, swarming sites, and social
behavior will help to determine which sites and during which seasons bat
populations need protection from human disturbance, which they are
especially sensitive to in most cases. Cooperation with recreational cavers
and speleologists will be essential to determine where swarming behavior
is occurring in the state, and in protecting these sites. Documentation of
the general dates for the beginning, peak activity, and end of swarming
sites, and the determination of where the bats are roosting during the
swarming season and during the winter in relation to the swarming site
will give an important framework for implementation of policies to protect
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bats when their populations are most vulnerable. A greater understanding
of the roosting behavior and preferences of temperate bats combined with
adaptive conservation management will help to ensure that Colorado bats
remain a part of the ecosystem in the future.
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