Tracking our vampire bats after they are released into the wild

After almost 2 years of cooperation experiments in captivity, we are now attempting to monitor the social relationships of our vampire bats as we release them back into the wild. We are hoping to track bat-bat and bat-cow encounters. To do this, we are attaching networked proximity sensors to 23 previously captive and captive-born bats with known social relationships and 27 new wild-caught female bats. We are then placing the cattle “prey” in a new location they have never been before. A grid of tracking stations will hopefully allow us to reconstruct their flight paths as they approach the cattle. We are also sampling their microbiomes to look at the microbiome similarity between bats within the colony, and at changes with the move from captivity to the wild.

This collaboration involves an international team of researchers including a very generous landowner, several local cowboys, two postdoc biologists (Simon Ripperger and Gerry Carter), two engineering students developing the software and hardware (Björn Cassens and Niklas Duda), several more engineers back in Germany, two field biologists helping with fieldwork and bat wrangling (Jineth Berrío-Martínez and Darija Josic), two PhD students doing the microbiome sequencing (Karthik Yarlagadda and Aura Raulo), and two principle investigators based in Panama and Germany (Rachel Page and Frieder Mayer).

The captive-born bats have apparently so far survived the transition to life in the wild (it’s their sixth day), but the tropical climate is putting the new technology to a difficult challenge. How well will the captive-born bats be integrated into the group? Will relationships formed in captivity be maintained in the wild? Do food-sharing bats also forage together? Hopefully, we will have some answers soon.

 

Here’s the post describing when we captured the bats from the roost (below).

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This project was funded by the National Geographic Society, the Smithsonian Institute, and the German Research Foundation (DFG).

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Final month in Panama

I have only one month left in Panama! We wrapped up data collection for our captive experiments, and we are now shifting to fieldwork. On June 28, I hired our last research intern for Panama, Darija Josic (MSc in Biology), a bat researcher from Croatia. She is helping both Sebastian Stockmaier and I with looking at effects of sickness behavior on contact calling, and she’s constructing an association network of our vampire bat group based on observations of physical contact while roosting (to compare with grooming and food sharing). She will later be helping Simon Ripperger and I track wild and previously captive vampire bats using proximity loggers.

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Through my university education, I have gained a good foundation in biology, with a focus in ecology, and later in physiology and immunology. During my studies I became a member of the Biology Students Association where my main interest were bats, and since then I have been actively involved in bat research. I took part in many field studies, often on surveys in Croatian National and Nature Parks. This is my first time in the tropics and I am discovering many amazing bat species living here.

I am contributing to the ongoing experiments on social behavior of vampire bats in the Rachel Page lab at STRI. The time that I am spending here at STRI working with Dr. Gerald Carter is an amazing opportunity to see first-hand how behavioral experiments are setup and executed and I have been learning a lot about data analysis. I had a chance to hear and meet so many great individuals working on a broad variety of research topics. In my future I hope to pursue further research on bats. The experience I’m gaining in Panama will help me tremendously in my career.


Angela Freeman (postdoc neuroendocrinologist from Cornell) is here this week to help us look at the neuroendocrine basis for social behaviors in bats. Angela has studied the mechanisms underlying communication and social behavior in many species including peacocks, ground squirrels, and pouched rats, and now fruit bats and vampire bats!

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Brunch to say ‘Farewell’ to Claire and ‘Happy Birthday’ to Jineth. Top row: Gregg Cohen, Gerry Carter. Bottom row: Michelle Nowak, Jineth Berrío-Martínez, Angela Freeman, May Dixon, Claire Hemingway, and Darija Josic


Today, Simon Ripperger and engineers Niklas Duda and Björn Cassens are arriving with their incredible high-resolution tracking system.

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More on both these projects (with Angela and Simon) in future posts…

 

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Meeting with the vampire bat control team, and footage of a white-winged vampire bat

On September 1, bat workers with the Ministry of Agricultural Development (MIDA) in Colon visited the Gamboa Bat Lab. We had an amazing and informative meeting and shared experiences working with vampires and other bats. We are hoping to develop some new long-term projects on vampire bats and discuss useful information to help solve the conflict between vampires and humans through inter-institutional cooperation.

El 01 de septiembre, personal de MIDA-Colon liderado por el Dr. Rogelio Singh visitó nuestro BatLab en Gamboa. Tuvimos una reunión increíble e informativa para compartir experiencias sobre murciélagos y vampiros. Esperamos desarrollar algunos nuevos proyectos a largo plazo sobre vampiros y discutir información útil para ayudar a resolver el conflicto entre vampiros y humanos gracias a esta cooperación interinstitucional.

–Jineth Berrío-Martínez

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My research assistant Jineth Berrío-Martínez organized a meeting between the Gamboa Bat Lab and the vampire bat control team at the Ministry of Agricultural Development (MIDA) in Colon. We talked about possible ways that they could help us by sharing information about relative abundance of vampire bats and/or rabies outbreaks, and that we could help them by sharing the latest research of vampire bat rabies, coming from disease researchers like Daniel Streicker and Daniel Becker. One of the most important lessons is to be sure to distinguish between the vampires and the more ecologically beneficial fruit, nectar, and insect-eating bats that spread seeds, pollinate flowers, and control insect pests.


 

While working with the MIDA crew, we caught a rare white-winged vampire bat (below), a species the team had not yet seen in Panama. We also saw another bat feeding on a chicken in a tree.

 

 

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Job opening: Animal Behavior PI position at Smithsonian Tropical Research Institute (also 3 ecology positions)

The Smithsonian Tropical Research Institute (STRI) has openings for 5 Staff Scientists. These are Principle Investigator positions where you run your own research lab as if you were a professor, but with minimal teaching duties. The STRI Staff Scientists pursue independent, internationally recognized research programs in the tropics. Example.

Previous tropical experience is not required. We are especially interested in hiring scientists in animal behavior, terrestrial microbial ecology, forest biology and marine science. The animal behavior position is below.

STAFF SCIENTIST RESEARCH POSITION IN ANIMAL BEHAVIOR

The Smithsonian Tropical Research Institute (STRI; www.stri.si.edu), headquartered in the Republic of Panama, is seeking an outstanding behavioral biologist to establish an independent world-class research program in animal behavior. The successful candidate will apply a deep understanding of natural history to resolve basic questions about behavioral mechanisms, evolutionary processes, and adaptive function. Areas of specialty may include, but are not limited, to behavioral ecology, evolution of behavior, sensory and neuroethology, chemical ecology of behavior, behavior developmental physiology and functional morphology, and the genetic basis of behavior. Candidates working on any animal taxa, marine or terrestrial, will be considered. Previous experience working in the tropics is not required. The successful candidate will have opportunities to mentor pre- and post-doctoral fellows drawn from an international community, and collaborate with the entire Smithsonian staff.

STRI has state-of-the-art research facilities, as well as terrestrial and marine field stations, and reserves throughout the country. There are environmental monitoring facilities, a large, multilingual support staff, and a library with extensive holdings in the natural sciences, as well as electronic access to all the Smithsonian libraries. The Republic of Panama and the adjacent regions of tropical America are phenomenally rich in terrestrial and marine habitats. The new staff member will join a vibrant scientific community of 30 staff scientists, and an international community of over 1500 scientific visitors per year, including fellows and interns supported through the Smithsonian. Staff scientists maintain diverse research programs covering ecology, evolution, physiology, development, and behavior of marine and terrestrial organisms and ecosystems, both ancient and modern, and the role of human interactions in shaping tropical environments. Staff scientists are not limited to conducting their research in or near Panama.

The position consists of full-time research. Internal funds are provided for laboratory setup, core ongoing research and travel. Staff scientists may supplement their basic yearly research budget by competing for additional intramural and external research funds. Staff scientists are evaluated on their research accomplishments. There is no official tenure, but rather a system of periodic reviews that allows for long-term research projects. For more information on working at STRI see the FAQ:

http://www.stri.si.edu/recruiter/users/jobs.php?id=184

No formal teaching is required, but in addition to mentoring post-doctoral fellows, students, and interns, STRI scientists are encouraged to teach in graduate training programs with affiliated universities, and to participate in outreach to local and international audiences.

 

Early- to mid-career candidates are encouraged. Annual salary is commensurate with experience. Compensation packages are internationally competitive, and include allowances to support educational expenses for dependent children at international schools. The position is based in the Republic of Panama. Relocation expenses are provided.

Qualifications: A Ph.D. and post-doctoral research experience in a relevant field, an outstanding publication record, demonstrated success in obtaining research grants, a history of successful collaborative research, and demonstrated skill in communicating science to the public.

To Apply: Please submit the following as PDF files: a cover letter, curriculum vitae, statement of research accomplishments and interests in animal behavior and related fields, PDFs of three to five significant publications, and the names and contact information of three references to strisearch@si.edu. Address inquiries to Dr. Rachel Page, Chair, Animal Behavior Search Committee, at PageR@si.edu.

Positions are open until filled; review of applications will begin on November 15, 2017 and interviews will commence shortly thereafter.

STRI is an equal opportunity employer and is committed to diversity in its workforce. Appointments are made without regard to nationality. In addition this position in animal behavior, STRI is currently filling staff scientist positions in terrestrial microbial ecology, forest biology and marine biology, and is supportive of the needs of dual career couples. For more information on the positions STRI is offering, please see our webpage: http://www.stri.si.edu/recruiter/users/jobs.php?id=184

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Behaviour17 Conference

Scientific conferences are some of the biggest highlights of my year. I just attended the Behavior2017 Conference in the beautiful seaside town of Estoril, Portugal.

Pictures Colour Library  - PCL

Estoril: warm sun, cool breeze and seawater

I’m still early enough in my scientific career that when I attend a conference, I often meet, for the first time, people whose work I’ve read. Public speaking is always a bit scary, but it’s such a joy to come together with people from all around the world who are working on similar, related questions in different organisms. There is not enough time to go over all the talks, but here’s a small sample.

Jonathan Pruitt gave an engaging talk on something he calls “social susceptibility” which is the extent to which the collective behavior of a social group is affected by a “leader” or keystone individual. In his remarkable social spider system, there are different discrete behavioral types (personalities), and introduction of a single extremely bold aggressive individual can make the entire colony more aggressive (more individuals attack). But this effect only occurs in deserts, not in the less dry savannah, because the aggressiveness of a colony is only advantageous in deserts. Pruitt tested whether the social influence of the bold individual (the leader) is determined by the traits of the leader or the followers. And apparently, it’s the followers that matter, not the bold leader. In deserts, the shy followers are influenced by a bold individual from either a desert or a savannah or even a heterospecific spider. In savannahs where aggressiveness is not adaptive, the shy individuals were not influenced by this extreme individual. Pruitt ended by making a general (obviously political) metaphor that influential “leaders” can only have be influential if the surrounding society as whole follows them, and varying levels of this “social susceptibility” can exist from group to group due to different selection pressures. As Pruitt put it, given high enough social susceptibility, a society can even be greatly influenced by a “heterospecific sham” (I found that bit hilarious). It’s a fun and complex story, and Pruitt told it well.

Another favorite talk was by my friend Neeltje Boogert on the effects of early life stress on social learning in zebra finches. Using a series of clever experiments, she and others found that when solving foraging “puzzles” young birds copy their parents, but when the young were given stress hormones, they stopped copying their parents and instead copied unrelated adults! Neeltje then did a similar study with song learning and found that young males tended to copy the song of their father, but the experimentally stressed juveniles did a worse job copying their father’s song. The stressed males had weaker father-son bonds and they may also have been more likely to copy non-father males. I wonder if similar phenomenon exist in humans: do highly stressed kids start learning earlier from their peers rather than their parents?

Another great talk was by Amiyaal Ilany, also about parent-offspring relationships in the context of social networks. Ilany had previously worked on a model exploring the idea of maternal inheritance of social networks (something I hope to test in vampire bats when I get a large enough sample size). Here, Ilany applied this idea to a huge long-term dataset collected by the Holekamp Lab from wild hyaenas. He showed that a hyena does indeed have similar network ties to her mother. This similarity depends on maternal social rank, in that offspring of mothers of higher rank inherit a stronger similarity to their offspring’s network position. The social inheritance of bonds also depends on the amount of time that the individual spends with their mother. One of the great thing about this study is that it shows where social network structure comes from.

I finally met Thomas Bugnyar (even if only for a moment). He gave a terrific talk on social cognition in corvids. He showed that ravens adjust their calling behaviour according to who was in the audience. The victims of an attack from another raven called more when their kin and bonding partners were present but called less when friends of the aggressors were in the audience. I’m a big fan of his work on social cognition and sociality in ravens and the corvids themselves.

Rene van Dijk gave a great talk on vocal kin signatures and kin discrimination in social weaverbirds. I’m hoping to look at paternal vs maternal kinship signatures in calls soon in vampire bats; I’ve been collecting data on this since 2009.

Sue Healy gave a great talk on the how birds build nests. There’s surprisingly many decisions involved about materials, colors, shapes and structures, and again, how early life experience can affect nest-building. I always love reading or hearing about cognition experiments, because the experimental designs are always so clever.

Barbara Taborsky discussed evidence from their cooperatively breeding cichlids about how a subordinate uses either helping or a submissive display to prevent aggression and eviction by dominants. The submissive display might somehow honestly signal that there is no challenge to the dominant. Interestingly, although the strategy can vary based on the immediate social context, there is consistent individual variation in strategy use. But it is not heritable. Instead, it comes about through something like a lifetime specialization into either ‘helper’ or a ‘submissive’ type based on early life experience. This later influences whether the subordinates either disperses, or stays and helps at the nest.

There were many other studies that manipulated the early environment and looked at effects on social behavior. For example, in zebrafish early environments influence social competence and gene expression in the brain years later.

Michael Taborsky gave some interesting new results on different cooperative strategies employed by cooperatively breeding cichlids, including reciprocity. I’m excited to see those papers when they come out. I’m hoping to do some experiments with reciprocity in rats next year.

There were several terrific posters from University of Exeter on cooperativeness in predator-inspecting guppies. They seem to have a really fantastic department there for animal behavior.

I enjoyed Dustin Rubenstein‘s “big picture” talk about comparing animal societies (including the often ignored taxa like spiders, thrips, and shrimps) to understand social evolution with some neat results from his work on snapping shrimp. It was great to finally see what these snapping shrimp look like! I’m really impressed with the number of systems that his lab works on in the field.

I had an interesting discussion with Dieter Lukas and Corina Logan about brain size evolution (see their recent review manuscript) and the necessity for open access (and other changes to publishing in science).

Yvonne Zurcher had an interesting poster showing evidence that vocal similarity influences the development of pair bonds in common marmosets (in addition to call convergence once bonds form).

Frans de Waal gave an entertaining talk with fun videos of nonhuman primates cooperating.

I have better appreciation for the idea of indirect genetic effects after this meeting.

Hanna Kokko, a leading theoretical biologist in evolution and ecology, gave a talk that changed the way I thought about evolutionary bet-hedging (which I mentioned at the start of my talk on “social bet-hedging”). I was a bit worried she would not like my rather loose use of the term “bet-hedging” but instead she seemed quite interested in my idea of how individuals invest in social relationships, which was very exciting for me. When we spoke I was a bit too nervous and star-struck actually. I think I stammered something like “I really love your book on modeling. But I’m really sorry…. I did not finish it…. I only made it to Chapter 3 when I was in grad school…” [And then maybe I trailed off because my brain was screaming: WHY ARE YOU SAYING THIS?]. Alas, this is one of those embarrassing moments that I’ll think about later randomly and shudder.

Barbara Koenig described her recent work on sickness behavior and its effects on social networks. This is of great interest to me, because we are now doing similar experiments in the vampire bats, led by Sebastian Stockmaier. The first paper should be out next year.

I took notes on far more talks and posters, but this blogpost could go on forever, so I’ll stop here.

There were several more prolific people I wanted to meet such Redouan Bshary and Frans de Waal. But so often I think to introduce myself, they are talking with someone else, and I started to think to myself, Do you actually have anything to say other than ‘I love your work!’ ?”. Then I would think, “What’s a good question I have for him?” … and then I start overthinking and then the moment is gone, hahaha. If I read enough papers that I like by someone, they eventually (and quite irrationally) begin to seem like some sort of celebrity to me. This is strange because I don’t generally like the idea of celebrities, focusing on people rather than ideas, but… it still happens. For better or worse, academia is just inherently social, with so many of phenomena that are being discussed at this very conference:

  • dominance hierarchies
  • networks of association with individuals greatly varying in centrality
  • leaders and followers
  • early career experiences that set individuals on different paths and specializations
  • reciprocity and other strategies for making cooperative investments while avoiding exploitation,
  • and (of course) “social bet-hedging“– the strategic tradeoff between investing in strengthening of existing relationships and creating new ones

 

Conferences give me a boost of inspiration. One of the main reasons I love conferences is that I get a lot of ideas while I’m sitting there listening to talks, or from the talk itself, or from conversations with people. In my crazy busy life at Panama, I almost never have time to just sit and think about ideas; I’m always caught up in the details of a particular experiment.

The next meetings I hope to attend are something called “CBEN 2017” and this one, both on social complexity and cooperation.

 

 

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molecular evolution in vampire bats (video)

More information: Sears Lab

 

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English translation of Park (1988) Dominance relationships in a colony of vampire bats. Korean Journal of Zoology.

Rachel Crisp is currently writing her masters thesis on dominance interactions in female vampire bats. Males have a clear dominance hierarchy in competition over roost territories, but do the female vampires have a dominance rank? If so, does it strongly correlate with cooperative interactions? Her work should come out next year!

Despite all the work on cooperation, not much is known or published about competitive interactions in female vampires. Interestingly, female vampire bats are larger than males, but there is no evidence for a strong female reproductive skew as in cooperative breeding societies. The little bit on competitive interactions that is available is in German (work in the 1970s supervised by Uwe Schmidt) or Korean (by Shi-Ryoung Park). Rachel Moon graciously translated this 1988 paper by Park from Korean to English.

For easy accessibility, here it is below.

Dominance relationships in a colony of vampire bat, Desmodus rotundus

Park, S.R.

Korea National Univ. of Education, Chongwon (Korea R.). Dept. of Biology

Translated by Rachel Moon, Harvard University

Originally published as Park, S. R. (1988). Dominance relationship in a colony of vampire bat, Desmodus rotundus. The Korean Journal of Zoology. 31 (4): 243-250.

 

ABSTRACT

Dominance relationship was investigated in a captive of Desmodus rotundus, a neotropical sangivorous bat, under seminaturalistic conditions. The hierarchy was determined from four different behaviors (flee, fly-out, avoid, wait) by the encounter of two adult bats on the feeding site. The aggressive action “flee after fighting” was relatively low (16%) compared to the other three observed behaviors. A hierarchy of the females was reflected sometimes in the feeding order. The harem male dominated the non-harem males and exhibited his territorial behavior. However, to his female partners he didn’t show aggression.

 

INTRODUCTION

Except for a few species, most bat species (Chiroptera) live socially (Gopalakrishna, 1955; Eisentraut, 1957; Kulzer, 1958; Goodwin and Greenhall, 1961; Barbour and Davis, 1969). Bats exhibit complex social structures and diverse kinds of social behavior (Bradbury, 1977). However, the functional significance of bat social structure and social behavior is still not well studied; therefore, this study aims to understand the significance of complex social behavior of bats by studying dominance relationship in a group of South American neotropical vampire bats (Desmodus rotundus).

Vampire bats (Desmodus rotundus) have developed and adopted unique behaviors and physiological structures that enable them to feed on the blood of vertebrate animals. Vampire bats form long-term small colonies with highly developed social structures (Wimsatt, 1969; Schmidt et a., 1978; Wilkinson, 1985). Until now it has been nearly impossible to study dominance relationship structure of vampire bats in natural settings; therefore this study aims to investigate dominance relationship in a group of vampire bats in experimental settings that resemble naturalistic conditions.

 

MATERIALS AND METHODS

This study was conducted with 9 vampire bats (Desmodus rotundus; three males, six females). Only one male and one female were captured in the wild (Colombia, 1975), and others were born and raised in captivity. The bats were kept in a thermostatic chamber (with 12h/12h of light and dark) at a temperature of 25C and 70% humidity. They were provided cow or pig blood (with removed fibrin) on a bird water feeder. In order to distinguish each individual from another, I marked each bat by attaching aluminum loop of different colors on its forearm (Table 1).

The observation cage had a size of 250 x 180 x 100 cm, and its left side, right side, back side and ceiling were made with thin plastic surface with small holes so that the bats could hang easily. The front center part of the room was made with transparent glass (100 * 50 cm) so that the experimenter can observe easily.

In order to observe the bats’ behaviors, an infrared night vision scope (metascope 9902E) was used, during early hours (17:30-20:30) of the 12 dark hours. This study emphasized an understanding the quantitative aspects of behavior observed in a previous study of vampire bat social relationship (Schmidt and Manske, 1973). In other words, I recorded and analyzed frequency and duration of observed behaviors, distribution of behaviors, and subsequent behaviors.

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Table 1

RESULTS

The social behavior of bats takes place at a feeding site, where they often encounter one another. During the initial period of feeding time, aggressive physical fights were often observed. This behavior usually begins with two bats pushing and shoving each other. If the opponent does not back off immediately, this aggressive physical fight occasionally turns into a fierce combat. To first determine the feeding dominance relationship of bats in the colony, we investigated the feeding times of individual bats, as seen in Figure 1.

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Figure 1

D (female) always feeds first; this female kept her place until she was full, even though other younger bats who were feeding at the same time often obstructed her by physical fight of pushing and shoving aside (Figure 2A). H (female) always showed up at the feeding site after the first feeding activity period, when other bats were mostly not feeding. During this period, H often encountered her 15-month-old daughter J at the feeding site. J would often push H to the side, although J had several unoccupied feeders nearby. Then J would wait right behind her mother H until H finishes feeding and returns (Figure 2B). As soon as H left the feeding site, J started to feed at the same spot H was feeding.

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Figure 2 (sadly unclear) and Table 2

However, not all of the other colony members ate their meals following such straightforward feeding order. Depending on each feeding site situations (whether bats are at the feeding site or not, and if so which bats are present), the bats visited the feeding site at irregular intervals. Therefore, it was difficult to determine group dominance relationship solely based on feeding order. Because the bats frequently encountered different individuals at the feeding site, it was possible to observe several types of social behavior. I chose four different types of social behavior exhibited by two encountering bats as the main parameter to determine bats’ dominance hierarchy.

  • Flee (after fight): After two adult bats meet and fight at feeding site, the winner bat continues feeding or starts to feed, whereas the loser bat flees away. For fighting behaviors, I observed shoving and pushing to the side, and attacking behavior.
  • Fly-out: It is a behavior shown when the inferior bat immediately flies away without showing any aggressive behavior when two bats encounter at the feeding site.
  • Avoid: When an inferior bat is feeding and another bat approaches, the inferior bat gives up its meal and moves to a different feeding site. The inferior bat feeds at a new feeding site or stands for awhile at a distance.
  • Wait: The inferior bat waits at a nearby place, or goes back and forth hesitantly at a different place, until the superior bat finishes feeding and leaves.

Fleeing is exhibited after aggressive behavior, whereas fly-out, avoid, and wait behaviors are “direct-flight” behaviors performed by inferior bats themselves in order to avoid potential conflicts; therefore, these three types of behavior are characterized as unaggressive or submissive behavior.

A total of 294 encounters were observed at the feeding site, and the frequency of each behavior type is shown in Table 2. Aggressive behavior accounted for 15.6% of all observed behaviors, which shows that it happened relatively less frequently than unaggressive behavior (Figure 3). Aggressive behaviors between male bats at the feeding site rarely took place; the most common behavior between two encountering male bats was “fly-out” behavior, which accounted for half of all behaviors exhibited.

In order to determine dominance relationship, I used a point system in which the superior (winner) bat earns 1 point when superior bat and inferior (loser) bat are distinguished. The score difference between two bats is shown in Table 3 by comparing the scores of each bat. Using this result to build a sociogram of dominance hierarchy at the feeding site, the following phenomena in each group could be explained.

Dominance relationship among harem females (Figure 4)

When encounters took place between two females from five harem females, the most common social behaviors were “wait” and “avoid.” D was the most superior dominant bat among five harem females. B, who had the lowest dominance hierarchy ranking, exhibited “wait” and “avoid” behavior as a response to D’s behaviors. E had a middle dominance hierarchy ranking, which was higher than inferior bats C and B and lower than superior bats D and H. E responded by “fly-out” behavior all three times when she encountered H. Although I never observed direct encounters of H and D at a feeding site (their feeding period almost never overlapped), I concluded that D had a higher dominance hierarchy ranking than H depending on feeding ranking.

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Table 3, Figure 3, and Figure 4

 

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Figure 5

Dominance relationship among males (Figure 5)

When two out of three male bats (G, A, F) encounter at the feeding site, the inferior bat usually flees away. Thus a clear dominance hierarchy was revealed among these three males. The most superior bat was G; whenever A or F appeared at the feeding site, G forced them to leave the site. When G approached, the inferior bats rushed their feeding. The most inferior bat was F; whenever F was feeding, I often observed him looking around his surroundings and rushing his feeding. Similarly, A also exhibited typical feeding behavior of inferior bats, which was carefully approaching feeding sites, quickly feeding non-stop, and leaving in a hurry.

Out of 31 encounters between G and A at the feeding site, A showed “fly-out” response 26 times; of 42 encounters between G and F, F responded by flying out 32 times. Out of 12 encounters between A and F, F exhibited “fly-out” behavior in all encounters. Therefore it was determined that the most superior bat was G, the most inferior bat was F, and A was in the middle.

Dominance relationship among male bats and harem females (Figure 6)

At the feeding site, G (male) always showed passive behavior towards old harem females who have previously given birth to pups. When these females were feeding at the feeding site, G responded by exhibiting “wait” behavior 30-40 cm away from the site until the females finished feeding. I observed six encounters between G and B (female who hasn’t yet given birth), and four out of six times B showed submissive behavior (“fly-out”) towards G.

A (male) showed dominance towards B and C (females); however, the number of encounter between A and D or H (females) was too small to clearly determine their dominance hierarchy.

F (male) was certainly superior than B and C (females), who had low dominance hierarchy rankings within harem females. However, he ended up getting an inferior status after frequent pecking-order disputes with other harem females. His dominance hierarchy ranking was determined by his fights (“fleeing”) with other females, which were 19 times (73%) out of 26 encounters.

 

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Figure 6

DISCUSSION

Vampire bats (Desmodus rotundus) form small groups when they go out to feed in the wild. Greenhall et al. (1969) observed behaviors such as combats, waiting, and co-feeding when vampire bats were feeding in groups in the wild. Furthermore, even in captivity the vampire bats often engage in pecking order disputes at feeding sites; therefore, the social structure based on dominance hierarchy seems to be a prominent characteristic of social behavior of vampire bats (Schmidt and Van de Flierdt, 1973). Vampire bats maintain close relationships through various social interactions at feeding sites, such as combats and submissive behaviors. According to the results of this study on a captive group of vampire bats, aggressive behavior (16%) took place less frequently than unaggressive behavior (submissive behavior), and most of the bats showed defensive or submissive behaviors (wait, fly-out, avoid) at the feeding site.

Park (1986) reported that aggressive behaviors are usually triggered by subadult bats, showing a strong tendency to claim high dominance status. Park observed that bats who are 14-16 months old often engaged more in dominance ranking fights compared to adult bats. The results of this study also revealed that group members abide by dominance hierarchy through a single consistent order when feeding and that aggressive behaviors between adult bats at feeding sites did not occur as often. Thus, it can be thought that vampire bats have especially well-developed mechanism of group formation, which serves to restrain mutual aggression by strengthening the cohesiveness among group members.

Vampire bats form a typical harem social structure (Load, 1976). Such social structure has been observed in other bat species such as Pipistrellus nanus (O’Shea, 1980), Phylolostomus hastatus (MaCreacken and Bradbury, 1981), Carollia perspicillata (Porter, 1979), and Artibeus jamaicensis (Morrison, 1978); the male bats in these species also form a single distinct dominance hierarchy, which is observed by ritualized combats. Park (1986) found out that alpha male (harem male) vampire bats stayed with females for a long period of time, whereas beta males stayed at a place where females use as their temporary shelter. On the contrary, gamma males stayed far away from female groups and did not exhibit any territorial behavior. Connecting to the results of this study, it seems that hierarchy system of male vampire bats is associated with territoriality. In the context of dominance behavior, Wicker and Uhrig (1969) observed Lavia frons engaging in a territorial fight with neighboring bats, and Bradbury and Emmons (1974) witnessed Saccopteryx leptura driving out outsider bats from its hunting territory. Several other bat species (Vespertilionidae: Dwyer, 1970; Brosset, 1976; Phyllostomatidae: Fenton and Kunz, 1977; Porter, 1979) are known to defend their harems and exhibit territorial behavior towards intruders and competitors.

Sex and age of bats are significant factors in formation of dominance hierarchy. Usually, older animals show dominance over younger animals, and males show dominance over females (Immelmann, 1983). This study reveals that alpha males (harem males) did not exhibit absolute dominance over females; on the other hand, harem males exhibited inferior behaviors toward their female partners. It is not easy to declare dominance relationship based on age only with the results of this study. Whether juvenile bats depend on dominance hierarchy rankings of their mother bats require further investigation.

References

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