“Prepared learning” in bats

I had a brief discussion with someone at the International Behavioral Ecology meetings about evidence in bats for prepared learning–the phenomenon that animals learn some associations faster than others. More importantly, the notion here is that animals learn things faster when those lessons would be most common and necessary in the environments in which they evolved.

The classic example is that a rat quickly associates feeling sick with a novel flavor of food, but it’s slower to associate feeling sick with a novel sound or sight [1]. Conversely, the rat learns faster to associate an electric shock with a novel sound or sight than with eating a novel flavor.

Most psychologists consider this quite special and call it an “adaptive specialization for learning” and even find it quite controversial or unbelievable [2]. I, on the other end of the spectrum, think most learning probably works this way. We just haven’t done enough studies on this topic which make that clear, because it’s difficult to show.

What’s truly impressive is that one form of prepared learning has been experimentally evolved in fruit flies  [3].

Two years ago, Dunlap and Stephens did a great experiment [3]. They created artificial worlds where flies were selected to learn to avoid an egg-laying site that was previously paired with quinine (which had been done before); and in addition to this, they created selection that favored learning some associations more readily than others.

To do this, they created two egg-laying sites that differed in both smell and color. In some worlds, the association of quinine with color was the best predictor of which type to avoid; in others the association of quinine with odor was most adaptive. That is, their experiment made one type of cue (odor or color) a more reliable indicator of flavor of quinine, which indicated that your eggs would not survive. In world 1, quinine was always indicated by the color of the food dish and odor was only half as reliable. In world 2, quinine was always indicated by an odor and color was only half as reliable. In worlds 3 and 4, both were either reliable or unreliable.  For 40 generations of evolutions, they allowed 10 populations of flies to evolve in each world. And yes, they found that when only odor associations were 100% reliable, the flies evolved increased sensitivity to learning the quinine–odor experience and reduced sensitivity to learning quinine–color. And the same was true for the other three worlds. In other words, these flies were born prepared to learn some things faster than others.

So there’s another reason to throw “nature vs nurture” out the window. In my opinion, natural selection doesn’t just give you the ability to learn, it gives you adaptively biased learning. Nature determines how you respond to nurture.

I really don’t think it could be any other way. You can’t build a general associative learning machine that pairs any information with any outcome based on repeated pairings. You can only build a machine that takes certain selection of sensory inputs and pairs those with other selected inputs to produce outputs. If A + B, then do C. But an animal has countless number of sensory inputs during every second of it’s life. Learning is always based on rules (about how to learn and what to learn) that are not themselves learned. So in some sense, it can be argued that all learning is in some degree prepared; it’s just a question of how much.

We can also see evidence for prepared learning in how animals learn today. Evidence for this comes from the niche-specific cognitive strategies hypothesis, put forth by York Winter, which predicts that animals feeding on stationary food like flowers (or that cache food in different locations [4-5]) will be faster to learn rewarded locations, whereas animals that feed on very mobile food (like insects) will be faster to learn rewarded sensory cues (like a visual cue for a predatory bird or an echo-acoustic shape cue for a predatory bat).


The neotropical bat, Glossophaga soricina (shown left) feeds on both insects, fruits, and floral nectar, but it possesses morphological and cognitive adaptations for flower-feeding. These bats will revisit the same flower as many as 30 times in a single night [7]. As expected from the niche-specific cognition hypothesis, Glossophaga has an excellent spatial memory that can overshadow sensory cues [8-9]. The bats can learn a rewarded location instantly, but they cannot ignore location and learn only using shapes. Even when spatial cues to the location of food become unreliable, Glossophaga has great difficulty in learning to ignore location and use shape cues instead [8]. In a study by Stich and Winter [9], bats were presented with choice between two very different shapes, one rewarded and one unrewarded, and the arrangement of shapes were swapped from left to right (see image below).


All you have to do is figure out that the sphere (left) always gives you food and the other shape never does. How long will this take you? 5000 trials and you still get it wrong 1 out of 10 times? WTF.

So all the bats had to do was learn to associate a shape with food. According to associative learning theory, this should be pretty trivial.

But here’s the shocker: In this simple task, Glossophaga required more than 5000 trials before reaching a criterion of 85% correct responses [9], because they could not ignore which side it was presented on. And when they were tested in a new experimental room, they forgot what they learned about shape in the old room [9].

This is astounding because we know that flower bats use shapes a lot to identify flowers and find flower openings. In fact, the shapes of some bat-pollinated flowers evolved to signal bats.

Learned spatial cues can even be more powerful than cues that are instinctually attractive. Many neotropical flowers that are pollinated by bats produce a compound called dimethyl disulfide, which is powerfully and innately attractive to these bats [10]. If you take a test tube of dimethyl disulfide into a cage of captive Glossophaga that have never smelled it before in their life, they will fly over and stick their head into the test tube. They love it even without any previous experience.

But once Glossophaga learns a rewarded location, their spatial memory will still overshadow their use of dimethyl disulfide. I did this experiment myself [11]. I was surprised. If you move a feeder over a few feet, they will fly  and hover at the blank spot on the wall where the feeder used to hang, before going over to the feeder clearly marked with rewarded smells and shapes.

The niche-specific cognitive strategy suggests that animal-eating bats should learn in a completely different way because prey don’t stay still. So sensory cues should be salient and learning food rewards based on sensory cues should be very easy for predatory bats. They should learn food-rewarded shapes or sounds faster than rewarded locations. And this seems to be true. Siemers [12] reported supportive evidence from a single insectivorous bat Myotis nattereri that quickly and easily learned to ignore location and associate shapes with food. They are the opposite of Glossophaga.

I  copied and pasted the relevant part below because this paper is hard to get online. I just love how Bjorn Siemers turned a possible mere anecdote into a nice little study using careful observation and on-the-spot experimentation. People who say you can’t really learn anything from a sample size of one, take note. He reports [12]:

…a female M. nattereri lost its balance and slid into a white round bowl next to the cage. The bowl contained about 250 mealworms. The bat grabbed a mealworm and flew off. The bat returned in a few seconds and approached the bowl, striking its uropatagium [tail membrane] against the rim of the bowl. The bat repeated the approach flight three times, retrieving one or two more mealworms. I then moved the bowl in the flight tent and started videotaping the bat’’s behavior. When the bat flew by the bowl at the new position, it hovered around it for 240 s without touching it. Over the next 60 min, the bat spent 650 s in eight 30 to 150 s long hover-and-attack- bouts above and around the bowl. The bat ‘attacked’ the bowl 101 times by touching the inner or outer side of the rim with its uropatagium. When the bat touched the inner side of the bowl, it sometimes successfully caught a mealworm in the uropatagium…

screen-shot-2016-09-11-at-7-52-00-pm…I then removed the bowl and put three alive and moving mealworms onto the smooth cardboard surface where the bowl had been. The bat inspected the site for 100 s without landing or touching the surface or catching any mealworms. When I placed the round bowl (now without mealworms) back onto the cardboard, the bat ‘attacked’ the empty bowl (13 times in 120 s). I filled the bowl again with mealworms and the bat ‘attacked’ the bowl another 28 times (three hover-and-attack- bouts with total duration of 180 s). Subsequently I initiated a choice experiment whereby at the opposite edges of the cardboard surface, the round bowl (empty) was presented simultaneously with the square one, new to the bat but filled with about 250 live mealworms. The rustling mealworms were clearly audible at least to my human ear from where the bat hovered over the experimental set up. The bat was tested during two hover-and-attack-bouts in this choice experiment (duration of bouts 110 s and 130 s, respectively). The position of the bowls was exchanged between the two bouts. While 20 ‘attacks’ were directed at the round, empty bowl, only two (unsuccessful) ‘attacks’ occurred at the quadratic one with mealworms (Fig. 1). The bat significantly preferred the empty [round] bowl as a target over the square one (χ2 = 14.7, d.f. = 1, P < 0.001). In the next night, I again presented the round, empty bowl on the cardboard. The bat ‘attacked’ three times in one 20 s hover-and-attack-bout and then lost interest

…After one accidental experience, an experimental bat learned to associate the round bowl with prey. The bat never attacked mealworms on the cardboard where the round bowl had been, and rarely did it look for mealworms in the square bowl that was unfamiliar to it as a feeding site. But the bat readily and repeatedly tried to retrieve prey from the round bowl, making attempts to take prey even when the bowl was empty. The evidence suggests that the bat was not perceiving the meal worms themselves but was operantly conditioned to the bowl as an indication of prey.

This finding was replicated and extended by Hulgard and Ratcliffe [13] who trained four additional bats of this species using rewarded styrofoam shapes hung from the ceiling.  All the bats learned to associate a specific shape with nearby food rewards and their shape training even seemed to overshadow their use of spatial memory.

So we have a flower-visiting bat that takes just one trial to learn a location and 5000+ trials to learn a rewarded shape, because spatial cues overshadow shape cues. By contrast, we have an insect-eating bat that takes just one trial to learn a shape, and once learned, this interferes with later spatial learning.

In the lab I’m currently in, Rachel Page has done a decade of research on how frog-eating bats use different cues and combinations of cues under varying contexts for finding their prey. But what we still need is one large comparative study using the same design across more species, as has been done with this massive comparison of cognitive self-control in primates [14].

Even better than just testing use of different cues (spatial, visual, echo-acoustic shape, smell, etc) would be testing the association rates between different cues and their natural outcomes. For example, a flower bat should readily match a location with either a food reward or an “escape-from-danger” reward (i.e. learn a hiding spot). In contrast, an insect-eating bat might more quickly learn to associate a location as a hiding spot than as a place to get food. Experiments like this would test that associative learning is influenced not only by the cue salience of the learner (determined by the ecological challenges it faced during its evolutionary history) but also on the ecological validity of the association itself (certain associations, like taste-sickness, simply make more ecological sense).


1. Garcia, John, and Robert A. Koelling. “Relation of cue to consequence in avoidance learning.” Psychonomic Science 4.1 (1966): 123-124.

2. Macphail, Euan M., and Johan J. Bolhuis. “The evolution of intelligence: adaptive specializations versus general process.” Biological Reviews of the Cambridge Philosophical Society 76.03 (2001): 341-364.

3. Dunlap, Aimee S., and David W. Stephens. “Experimental evolution of prepared learning.” Proceedings of the National Academy of Sciences 111.32 (2014): 11750-11755.

4. Clayton, Nicola S., and John R. Krebs. “Memory for spatial and object-specific cues in food-storing and non-storing birds.” Journal of Comparative Physiology A 174.3 (1994): 371-379.

5. Brodbeck, David R. “Memory for spatial and local cues: A comparison of a storing and a nonstoring species.” Animal Learning & Behavior 22.2 (1994): 119-133.

6. Clare, Elizabeth L., et al. “Trophic niche flexibility in Glossophaga soricina: how a nectar seeker sneaks an insect snack.” Functional ecology 28.3 (2014): 632-641.

7. Winter Y, von Helversen O (2001) Bats as pollinators: foraging energetics and floral adaptations. In: Chittka L, Thomson J, editors. Cognitive ecology of pollination. Oxford: Oxford University Press.. 360 p.

8. Thiele J, Winter Y (2005) Hierarchical strategy for relocating food targets in flower bats: spatial memory versus cue-directed search. Anim Behav 69: 315–327.

9. Stich KP, Winter Y (2006) Lack of generalization of object discrimination between spatial contexts by a bat. J Exp Biol 209: 4802–4808.

10. Von Helversen, Otto, L. Winkler, and H. J. Bestmann. “Sulphur-containing “perfumes” attract flower-visiting bats.” Journal of Comparative Physiology A 186.2 (2000): 143-153.

11. Carter, Gerald G., John M. Ratcliffe, and Bennett G. Galef. “Flower bats (Glossophaga soricina) and fruit bats (Carollia perspicillata) rely on spatial cues over shapes and scents when relocating food.” PloS one 5.5 (2010): e10808.

12. Siemers, Björn M. “Finding prey by associative learning in gleaning bats: experiments with a Natterer’s bat Myotis nattereri.” Acta Chiropterologica 3.2 (2001): 211-215.

13. Hulgard, Katrine, and John M. Ratcliffe. “Niche-specific cognitive strategies: object memory interferes with spatial memory in the predatory bat Myotis nattereri.” Journal of Experimental Biology 217.18 (2014): 3293-3300.

14. MacLean, Evan L., et al. “The evolution of self-control.” Proceedings of the National Academy of Sciences 111.20 (2014): E2140-E2148.

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Summer 2016 updates

Our two undergraduate interns Yeli Garcia (Earlham) and Emily Dong (Cornell) just completed their independent projects and finished their seasons in Panama. Yeli’s project was entitled “Guano scent as a cue for roost-finding in vampire bats” and Emily’s was “Co-feeding and food sharing in vampire bats”. They both worked hard, did a terrific job, and I’m quite proud. Emily and Yeli were funded by NSF through the Research-for-Undergraduates (REU) program.

PhD student Sebastian (Basti) Stockmaier (UT Austin) also wrapped up data collection for his project on inducing sickness behavior in vampire bats and measuring the effects on physiology and cooperative behavior.

Undergraduate intern Rachel Moon (Harvard) is currently working on linking contact call structure of vampire bats to group membership and kinship.IMG_0896Above: Yeli Garcia, Emily Dong, Gerry, Basti Stockmaier, and Rachel Moon

Earlier in the year, PhD student Gloria Gessinger used hi-speed video and ultrasonic recordings to test whether vampire bats produce echolocation calls through the nose or mouth. PhD student Andrea Rummel also did some pilot tests of how vampire bats land on the ceiling. Postdoc Simon Ripperger conducted a pilot study tracking wild vampire bats with proximity sensors.

Screen Shot 2016-08-14 at 9.57.18 AM

Above: Simon and I setting up base stations for automated data collection from free-ranging vampire bats.

During his time here,  Simon placed cameras on the ground outside of several tunnel roosts to look at frog-eating bats coming and going. One of the roosts was also home to a lone male vampire bat who detected the camera immediately (see video below).

In collaboration with Damien Farine and Gabriele Schino, I will soon be writing up a study on detecting the relative ease of reciprocity and kinship effects using data from vampires and primates. Finally, my two long-term projects on 1) reciprocity and 2) development of novel food-sharing bonds will continue into next year.

My work in Panama to date has been conducted in collaboration with my co-PI’s Rachel Page (STRI) and John Ratcliffe (U Toronto), and I’m currently applying for new postdoc fellowships.

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Recent media article about vampire bats and friendship

Sapiens Magazine just put out an article about vampire bats and friendship.

Screen Shot 2016-08-11 at 11.26.02 AM

The author Leah Shaffer did a great job, probably the most accurate media story on the vampire bats I can remember. Usually, journalists get a lot wrong, but they did a great job fact-checking this one.

Also, below is an edited transcript of some of the email interviews connected to this article which don’t make it into the article. I paraphrased the questions I was asked, and re-arranged or deleted some of them.

Does your research tell us about cooperation in general or in humans?

I do think the vampire bats can give us general insights into how cooperation works in a network of social relationships. Mostly this is due to their cooperative behaviors being easier to measure and manipulate compared with say people and other primates. They are small like lab rats, and cooperative behaviors like grooming and food sharing take place in a small dark corner of a cave or tree, so you can simulate that in captivity.

But clearly, human social networks are quite different and more complex than vampire bat food-sharing networks!

One issue in human cooperation is that between-tribe competition can mask the nuances of within-tribe competition. People focus on in-group vs out-group behavior. But clearly, people have differing relationships also within their in-groups.

You should contact Robin Dunbar. He is a prolific and influential author on the topic of the evolution of human social networks.

Where do you study the bats in Panama?

I captured them in Tole, Panama (at a roost on a cattle pasture) and brought them to the Smithsonian Tropical Research Station in Gamboa where I keep them in captivity.

Why do you not consider the food-sharing to be “communal”?  

“Communal” implies that something is shared (roughly equally) throughout a community. The bats share exclusively with their family and friends–with specific individuals more than others within a roosting group. They are more nepotistic than communal. The bat’s social network is not the same as the group it roosts with.

Are scientists trying to find the friendship gene?

It is very silly to say that there might be a “friendship gene”. So I think that sounds bad, simplistic. Some science writers will say someone found, say, a “vision gene” but what that really means is that there’s a gene that turns on another gene that encodes a protein (one of many) that the eyes need to function properly. So if you mutate that gene, the individual is blind. But calling that a “gene for vision” is misleading.

There are no genes for complex traits or behaviors. Like, say you need say 10,000 different chemicals to bake a chocolate cake, and if you discover just one of them (like sucrose), it makes no sense to say “we found the chocolate cake molecule”. The whole idea of a “cake molecule” doesn’t even make sense. Even the whole list of molecules should not be called “cake molecules” because you can make many other things with those same molecules. Same is true for “vision gene” or “friendship gene”.

Friendship is even more complex than the chocolate cake example, because friendship is not a physiological structure or even a trait of a single individual; it is an emergent outcome of the behavior of two individuals (or more). Differences in behavior are also influenced by differences in the brains among multiple individuals.

I’m not doing anything with genetics or brain differences underlying cooperative traits at the moment. Hopefully, someday in the future we will see the brain work linking hormones and neurotransmitters and their receptors to the behaviors. After that, we might then look at changes in the genetic sequences that build the receptors. That would be more than 5 years away I think. It’s not happening in the next 2 years (unless someone gives me a giant pile of money after reading your article). I’ve decided I would also rather collaborate with a neuroscientist and have them do the work.

What I’m hoping to do next is to work on how food-sharing bonds might extend to other kinds of behaviors outside the roost, like feeding from the same wound. I plan to work with a German team (a guy named Dr. Simon Ripperger) to put tiny computers (smaller than 2 gram) on the backs of vampire bats. The computer backpacks communicate with each other wirelessly, and with a wifi base station, and log the distance and time of social encounters. All the data can be collected remotely. That way, we can study captive bats and then keep tracking their social interactions after we release them into the wild. We hope to gain insights into social foraging in vampire bats. Social foraging and wound-sharing outside the roost should help explain social grooming and food-sharing relationships within the roost. Stuff like that.

Can you briefly explain what “social grooming” is?
Social grooming is when one animal grooms another. Social grooming is rare in most bats.

I did a study showing that non-vampire bats kept in the same situation spent no time or very little time (under 1% of their awake time) licking the fur of other bats, even when they were stuck together in captivity for their whole lives. That fur licking might just be bats licking food off another bat’s fur if they are messy eaters. Social grooming was 14 times higher in vampire bats and  it serves a social function.

In the the prairie vole research, did the researchers find all the genes for monogamy?
No, they found a key genetic sequence that will turn on and off the expression of receptors for brain chemicals that influence pair-bonding. So by adding or subtracting the  receptors (or the genes for it) they could turn monogamous behavior in males on or off. It’s amazing. That is simplifying it a bit. But that’s the gist.

You can study monogamous pair bonding at many levels in biology. Monogamous behavior differs between species, but also between populations. Across individuals, it depends on brain differences– the number and location of receptors on brain cells, which depend on gene expression, which depend on regulatory genes. They described that whole process from the species level to the genes. It is complicated, but let me try and break it down.

So DNA, genes, that encodes the proteins which link together to form a “receptor”– the receptor is on the membrane of a neuron. It is like a lock and molecules like oxytocin and vasopressin are neurotransmitters– the “keys” that fit into those “locks”. If the cell has the right lock and you put the right key into the lock, then you make that brain cell do something different. So a monogamous vole has those locks on cells in different amounts and in different regions of the brain. Having more locks on those brain cells makes those neurons more responsive to the chemical signals (hormones and neurotransmitters). This basic mechanism is very common in biology. For example, having different receptors for hormones throughout various body parts is what makes a male and female bodies develop differently. So this the same kind of thing, but inside the brain.

What does this all mean? It’s exciting. It means that we are beginning to understand how specific neural mechanisms (the key-lock stuff) lead to many of the differences in behavior between individuals–what we call “personality traits”. I think it’s truly transformational science, capable of changing the way we understand human nature. Eventually, in the distant future, personality will be largely understood as differences in the brain in just the same way that differences in running ability are understood as physical differences in lungs, blood, muscles, etc. I imagine a world where we would never say something like “this person is an evil person” and that’s the end of the story; we would instead say something like “this person lacks empathy for others because they lack oxytocin receptors throughout this region of their brain” or “this person had this traumatic childhood experience which led to these exact changes in their brain”. And maybe in the future we will treat such brain/behavior disorders more precisely, rather than what we do now, which is more like hitting your TV and seeing if the screen stops flickering.

Who did this research with the voles?
I can give you a list of names off the top of my head and you can dig further: Sue Carter, Larry Young, Steve Phelps, Alex Ophir, Tom Insel

Was the author wrong in distinguishing between “reciprocity, reciprocal altruism and “pro-social” behavior”?
Reciprocity and reciprocal altruism (I use these interchangeably) are not really examples or types of prosocial behavior. To me, they are hypotheses to explain why ‘prosocial’ traits are favored by natural selection. In other words, prosocial behavior can be explained by reciprocity, but not vice versa.

Prosocial behavior means you’re just helping another individual for whatever evolutionary reason. Authors start using the term “prosocial” to describe a behavior in an agnostic way without assuming an evolutionary explanation. Terms like “altruism” have a technical definition in the evolutionary literature that involves a decrease in lifetime reproductive success. So a behavior researcher can’t use that to describe a mere observation of helping without evolutionary biologists complaining. You could say “psychological altruism” but that suggests you know something about how the animal is thinking. So “prosocial behavior” makes no assumptions about evolution or psychology. It’s very confusing because different authors sometimes use these terms a bit differently. But I imagine that Joan Silk (or other leading experts on this topic) would agree with what I’ve written above.


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Revisiting Wilkinson 1984

In 1984, Gerald Wilkinson published a paper in Nature showing that vampire bats share food in the form of regurgitated blood, within groups that contain both kin and non-kin. This was one of the fi…

Source: Revisiting Wilkinson 1984

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Summer interns for the vampire bat project

Every season, two interns will be assisting the vampire bat food-sharing project at the Smithsonian Tropical Research Institute in Gamboa, Panama. These are our two STRI-funded interns for Summer 2016.

Emily Dong is a major in the Biology and Society, and will be starting her third year at Cornell (my alma mater). Emily is always positive, excited, and enthusiastic. Ever curious, she seems to absorb information like a sponge. She is linking feeding interactions between vampire bats with grooming and food-sharing, and testing whether specific bats follow each other to feeders.

What are your interests?

Beyond scrolling through socialbat.org, my interests revolve around examining relationships, especially friendships that occur across animals, whether it be humans or vampires. I’m intrigued by cooperative bonds, the behaviors that enable (or disable) social bonds, and how specific bonds have become evolutionarily persistent. I also like stories! A lot! Storytelling, from historical narratives to dinner table conversations, is a powerful way to share information and create (or maintain) social order.

What do you hope to gain from working on the vampire bat project?

I’m excited to spend quality time with vampire bats and observe the colony to the point of knowing specific bats’ unique habits. Besides working closely with bats, I’m hoping to see first-hand what the research life entails. (And I’m stoked to hang out with Gerry and other cool bat people, so that I absorb all their knowledge and coolness). 

What are your plans for the future?

My future holds many social bonds and much reciprocity, but whether I’ll partake in them, study them, or both is still undecided!


Yelitza Garcia is entering her final year at Earlham College driven by a passion for science and research that she has fostered since childhood. As a first-generation college student, she became interested in science after entering a science fair at the age of eight. Yeli is highly-motivated to get research experience and she plans to study animal behavior, evolution or ecology. Armed with valuable combination of being highly-motivated and ambitious without a drop of overconfidence or selfishness. She is working on the sensory basis of roost-finding in vampire bats.

What are your interests?

Like most young, starry-eyed, field ecologists, I have a deep-set admiration for being outdoors and learning about the world around me. I am primarily interested in behavioral ecology and conservation biology, but love to learn and read about vertebrate evolution and bioethics in my spare time. Other than reading, I love spending time outdoors hiking, climbing, and birding, and cooking for my loved ones.

What do you hope to gain from working on the vampire bat project?

In addition to interacting on a daily basis with these adorable flying furballs, I hope to learn as much as I can from this project about research as a career, behavioral ecology, and tropical communities. This is the first opportunity I have to do research full-time, so I want to learn about and contribute to meaningful discussions about reciprocity, sensory ecology and more. I have never felt as grateful or lucky as I am now that I get to wake up every day to do research and discover more about animal behavior.

What are your plans for the future?

After graduating from Earlham College this coming spring, I hope to attend graduate school and work towards a masters, and hopefully a doctoral degree in Ecology and Evolutionary Biology. Through the rest of my education and after, I hope to continue research and conservation work in the tropics. I am incredibly grateful for the opportunity to work on this project because this is the work I plan to dedicate my life to.


Figure 1. To test the effects of association, we began housing unfamiliar female humans Emily (left) and Yeli (right) together in close proximity within the same roost, and we have already observed cooperative behavior, including huddling and food sharing (shown above).


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Social inheritance in vampire food-sharing networks?

We are soon to be wrapping up several analyses and starting some new ones. I want to mention one analysis that never really got off the ground, but it’s a good idea. My intern Jana asked me a great question: Does a female vampire bat inherit some of her food-sharing partners from her mother?

This question has some really interesting theoretical work behind it. I looked into my PhD data a bit, but unfortunately, I don’t have the necessary sample size. Food sharing most often occurs among females, and I have focused my data collecting on females, but there were only 4 females born during my PhD study. And I have only poor data for the 15 males born during my study (I’ll say more about that sex ratio bias in another blogpost).

Anyhow, to look into Jana’s question, I just now measured the average donation rate to bat A from all 37 possible donors, then compared that metric for bat A’s mom. If you just look at whether bats have more similar sharing networks to their moms versus all other bats, you find that females (n=4) do, while the males (n=15) do not. But this does not prove anything. We should expect that females should have more similar connections to all other females just because females are more similar to females in general when it comes to food-sharing. So this might have nothing to do with maternal bonds. What we really want to know is: Is the sharing network of female bat A more similar to bat A’s mother than to the mothers of bats B, C, or D?

Answer: Nope. That was only true in one case. Under perfect social inheritance, the rankings of similarity of the four bats to their own mom should have been all 1st place (out of 4). Instead the rankings were 4th (last), 4th (last), 1st, and 3rd. Clearly, it’s too few observations to draw conclusions, but there’s nothing very striking here.

As we collect more data from more bats, it will be interesting to do a more powerful comparison of the sharing networks of mothers and their adult daughters. With more data, we can also ask whether adult bats with many sharing partners have adult offspring with many sharing partners.

In the next few months, we hope to be looking at how bats form new food-sharing relationships with strangers. And we also have three more new pups.

Here’s a picture of the Rachel Page Bat Lab/Family in Gamboa:


And here’s a preliminary association network of female (red) and male (blue) frog-eating bats (Trachops cirrhosus) based on 4 years of roost capture data (more on that coming soon!).

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Finally, some results of some recent cool papers:

Are there different cooperative social structure types? Or do animals socialize along a gradient? There are types! “Using phylogenetically informed comparative analyses, we found strong evidence indicating that not all reproductive arrangements within social groups are viable in nature and that in societies with multiple reproductives, selection favours instead taxon-specific patterns of decrease in the proportion of breeders as a function of group size.”

Do bacteria within your own gut cooperate with each other? Yes: “Using in vitro systems and gnotobiotic mouse colonization models, we find that extracellular digestion of inulin increases the fitness of B. ovatus owing to reciprocal benefits when it feeds other gut species such as Bacteroides vulgatus. This is a rare example of naturally-evolved cooperation between microbial species.”

Do individuals choose to cooperate based on expected payoffs?  “We experimentally created a situation of high conflict in communally nursing house mice, by using a genetic tool to create a difference in birth litter sizes. Females in the high conflict situation (unequal litter sizes at birth) showed a reduced propensity to give birth as part of a communal nest, therefore adjusting their cooperativeness to the circumstances.”

Do individuals pay attention and change their behavior depending on their own dominance status relative to that of others? “In this study, it is shown that male mice form linear dominance hierarchies characterized by individuals attacking in bursts. Temporal pairwise-correlation analysis reveals that non-dominant individuals avoid behaving aggressively concurrently with an aggressively behaving alpha male. This anti-correlation is only found with alpha males and is greater for more despotic alpha males. It is concluded that less dominant individuals modulate their aggressive behaviour in response to their social context, resulting in an attentional group structure.”

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New paper on vampire bat communication

Our newest paper is Common vampire bat contact calls attract past food-sharing partners in the journal Animal Behaviour. You can download the paper for free until June 12, 2016 here at this link: http://authors.elsevier.com/a/1SwLKmjLdkSa

It’s a simple playback experiment where we disentangled kinship and food sharing as predictors of a bat’s attraction to calls of different individuals. Subject bats chose between moving towards and spending time near two ultrasonic speakers pretending to be different bats. With the simulated callers were paired by kinship, we found that bats were biased to callers that had fed them more. But when callers were paired by sharing history, bats were not biased towards closer kin. The playback responses suggest that the vampire bats vocally recognized individuals, and this is a further illustration of how food sharing history can overshadow kinship in determining social bonds and behavior.

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