Field notes on weekend trip to Costa Rica (with disc-winged bats!)

Spix’s disc-winged bat Thyroptera tricolor has suction cups (yes, suction cups) on its thumbs, and it uses these to cling to the smooth surface of young, furled Heliconia leaves.

I’ve wanted to see a disc-winged bat since I was about ten years old, and I finally got to see them this week while visiting Gloriana Chaverri, and Caroline and Michael Schöner at their field site in Costa Rica over the weekend.

Gloriana is a leading expert on social lives of Neotropical leaf-dwelling bats. This includes bats that chew leaves to make them into “tents” as well as disc-winged bats (Thyroptera). Over the last seven years, Gloriana has shown that Thyroptera live in small groups with multiple matrilines that often switch between their very temporary roosts, the furled leaves [1-3]. Both sons and daughters often remain at their natal site, and inbreeding is avoided because the bats mate with members of other populations. Each population includes several groups that switch among several roosts.

Despite moving daily between their tubular leaf roosts, the bats maintain very cohesive social networks. To coordinate their roost-switching, the bats use a system of contact calling [4-7]. Bats flying in search of their group make one contact call type called an “inquiry call” and groupmates within furled leaves make another call type in response. The calls have both individual and group-level signatures. The calls are also amplified by the funnel-like shape of the leaf roost.

Here’s a video of one flying into a leaf roost:


Most recently, Gloriana has been working with Caroline and Michael Schöner. The Schöners have pioneered work on an astonishing mutualism in another leaf-dwelling bat [8-10]. There is a pitcher plant in the paleotropics (Nepenthes) that has coevolved with a small insectivorous bat of the genus Kerivoula. The bat lives inside the pitcher and defecates into the fluid-filled “pitcher”. Most pitcher plants are carnivorous. They trap, drown, and digest insects inside the tiny pool of their pitcher, but this pitcher plant is modified to be a tiny little one-bat house. The level of the digestive fluid is lower to accommodate the bat’s roosting position. The plant lets the bat do the capturing, chewing, and pre-digesting of the insect prey. Some pitcher plants also attract shrews with a nectar reward and get them to poop into the pitcher [11]. For lack of a more polite term, the Schöners call the plants “coprophagous”.

In exchange for nutrients, the plant benefits the bat by providing it with a literal “roof over it’s head” and it’s distinctive shape is acoustically attractive to the bats. This is yet another example of bat-plant acoustic communication. There are also bat-pollinated flowers and leaves that reflect and enhance the echolocation calls of bats when they are ready to be pollinated [12-13].

What’s especially intriguing is that Kerivoula will also live in a different pitcher plant species that is not coevolved for the bats, and the bats can only fit inside the pitcher because it has been emptied. How? Something chews a small hole at the base of the pitcher to drain the liquid out. Could it be the bat? Nobody knows for sure. The Schöners suspect this is the case, but they have not yet caught the bat in the act. The bat might be a mutualist for the first species, but a parasite for the other. Or perhaps there’s a three-way interaction: the bat, the pitcher plant, and a third mystery organism that makes the hole, perhaps to drinks the pitcher plant liquid. It’s an unsolved mystery.

See also this blogpost by Merlin Tuttle and photos.

The Schöners are surprised by the physical similarities of Thyroptera and Kerivoula, although the personalities of the two bats are quite distinct. Kerivoula will eat larger insects and has the bite to match. Thyroptera it seems are a bit easier to work with. After your experiments are done, you can release Thyroptera into a furled leaf and they will just crawl inside and stay. As Caroline puts it, “Thyroptera is more well-behaved.”

The Schöners are tracking the bats’ movements among different leaves in the wild. Do the same bats consistently find new leaves and others follow? Or do all the bats do a search on their own? They are also looking at the bats use of spatial memory when relocating roosts. For this experiment, they work in a flight tent with an array of artificial leaves. The work is fascinating and I’m excited to see the results.

The Schöners take turns tromping around in the forest looking for bats and staying at the field station looking after their 9-month-old, Sophia, who loves fried platanos and has inherited the Schöners’ love of smiling. One similarity between Gloriana and the Schöners is their friendliness and propensity for hearty laughing. The atmosphere at the field station is one of joyful cheer, with everyone trying their best to make Sophie smile. It’s been a great place for a holiday.

Before coming to the Baru field station where I am now, I visited two caves with my wife Michelle, my labmate Nia Toshkova, and our guide: Gloriana’s graduate student Stanimira Deleva, who is studying the variation in use of caves by all different Costa Rican bats. The larger caves was two kilometers long and full of Pteronotus gymnotus or Pternotus davyi. The smaller cave had Saccopteryx bilineata and Peropteryx kappleri. Nia and Stanimira are old friends, both cavers from Bulgaria. Michelle and I met Stanimira on a caving trip in Panama where I found a new potential site to work with vampire bats.

Here is a video of the Thyroptera being very cute:


  1. Chaverri, G., & Kunz, T. H. (2011). All-offspring natal philopatry in a neotropical bat. Animal behaviour, 82(5), 1127-1133.
  2. Buchalski M, Chaverri G, and Vonhof M. 2014. When genes move farther than offspring: gene flow by male gamete dispersal in the highly philopatric bat species Thyroptera tricolor. Molecular Ecology 23:464-480.
  3. Chaverri G. 2010. Comparative social network analysis in a leaf-roosting bat. Behavioral Ecology and Sociobiology 64:1619-1630.
  4. Chaverri G, Gillam EH, and Vonhof MJ. 2010. Social calls used by a leaf-roosting bat to signal location. Biology Letters 6:441-444.
  5. Gillam EH, and Chaverri G. 2012. Strong individual signatures and weaker group signatures in contact calls of Spix’s disc-winged bat, Thyroptera tricolor. Animal Behaviour 83:269-276.
  6. Chaverri G, Gillam EH, and Kunz TH. 2012. A call-and-response system facilitates group cohesion among disc-winged bats. Behavioral Ecology 24:481-487.
  7. Chaverri G, and Gillam EH. 2013. Sound amplification by means of a horn-like roosting structure in Spix’s disc-winged bat. Proceedings of the Royal Society B 280:20132362.
  8. Grafe TU, Schöner CR, Kerth G, Junaidi A, and Schöner MG. 2011. A novel resource–service mutualism between bats and pitcher plants. Biology Letters 7:436-439.
  9. Schöner CR, Schöner MG, Kerth G, and Grafe TU. 2013. Supply determines demand: influence of partner quality and quantity on the interactions between bats and pitcher plants. Oecologia 173:191-202.
  10. Schöner MG, Schöner CR, Simon R, Grafe TU, Puechmaille SJ, Ji LL, and Kerth G. 2015. Bats are acoustically attracted to mutualistic carnivorous plants. Current Biology 25:1911-1916.
  11. Clarke, C. M., Bauer, U., Ch’ien, C. L., Tuen, A. A., Rembold, K., & Moran, J. A. (2009). Tree shrew lavatories: a novel nitrogen sequestration strategy in a tropical pitcher plant. Biology Letters, 5(5), 632-635.
  12. von Helversen, D., & von Helversen, O. (1999). Acoustic guide in bat-pollinated flower. Nature, 398(6730), 759-760.
  13. Simon, R., Holderied, M. W., Koch, C. U., & von Helversen, O. (2011). Floral acoustics: conspicuous echoes of a dish-shaped leaf attract bat pollinators. Science, 333(6042), 631-633.
Posted in About cooperation, Other topics | 1 Comment

New paper: risk exaggerates nepotism in vampire bats

Here’s the paper.

In evolutionary biology, we often draw a line between “altruism” and other cooperative traits. Altruistic traits are special in that they lead to a net cost to one’s survival and reproduction. Some traits are clear cases: when a bee stings you it dies, so the suicidal bee sting is an altruistic trait.

But nature abhors clear categories. Most seemingly “altruistic” behaviors are ambiguous in whether they pose net average fitness benefits or costs. This leads to some confusion for several reasons. First, most acts that most people call altruistic are not altruism in the evolutionary sense. Any form of “reciprocal altruism” is not really altruism as defined above. This is why people who study animal cognition invented the term “prosocial” behavior to avoid the word “altruism” and all the inevitable semantic arguments with evolutionary biologists. Second, the kinds of costs we can easily measure (like time and energy) are not the same as fitness costs which can only be measured after whole lifetimes have gone by, so this means we can’t categorize most of the cooperative behaviors that we are studying. Third, many people equate helping kin with “altruism” but much helping between kin might actually be mutually beneficial. For example, natural selection might have shaped me to care about the survival of my family, not just because that helps them survive, but also because it helps my own survival.

For traits like this that pose both costs and benefits to the helper (food sharing in vampire bats is an example), it’s better to think of there being a spectrum where the exact cost/benefit ratios of a cooperative trait can slide around from positive to negative depending on the circumstances. It’s not a completely different behavior just because you move from -0.1 to +0.1 direct fitness effects.

Thankfully, to better understand a cooperative trait, we don’t always need to try to unambiguously classify traits or exactly measure the change in lifetime reproductive success that comes from performing the behavior. Instead, we can just change the factor we think is important and see if the animal’s helping decisions also changes as one would expect from theory. Rather than measuring lifetime fitness consequences, we can test the design of the trait. In this case, what information is involved the decision-making process?

For example, many animal parents will go to extreme lengths to protect their babies (e.g. below is footage of a mother moose attacking a truck) and various theories (inclusive fitness and parent-offspring conflict) makes predictions about the design of this behavior.

A mother’s brain should be designed by natural selection to put herself at some degree of risk to save her offspring, but not too much risk. Unlike the sterile worker bee, she is not a genetic dead-end, so she should not carelessly cast away her own life for any potential benefit to her genetic kin. Theory predicts that at some risk to her own survival and reproduction, she should give up on trying to save her offspring. There’s a risk factor that can be tuned up and down that should have an effect on the probability of A helping B, and this factor should interact with genetic relatedness. One could also tune up the kinship factor. As the famous quote by Haldane goes: I would give up my life to save 2 brothers or 8 cousins.

Risk should decrease my willingness to help and increase the degree to which I care about someone’s relatedness to me. As you dial down the risk, I am more willing to help: I would not run into a burning building, suffering certain third degree burns, to help a total stranger, but I would do it if I had protective gear. As you dial up the risk to me, the circle of people I would be willing to help in that situation should shrink: I would jump in the ocean to save a stranger, but I would only jump in shark-infested waters to save my child.

Like other animals, we don’t weigh the costs and benefits consciously, but the emotional urgency we feel to help or not help depends on situation-based cues that have, in our evolutionary past, acted as reliable indicators of inclusive fitness benefits of helping in situations similar to the one we are facing. 

So how can we test this in food-sharing vampire bats?

A few years ago, I was trying to record contact calls from hungry vampire bats. So put a caged hungry bat in a larger flight room with the other bats and put a microphone on it. I discovered to my surprise that other bats would feed these trapped individuals through the cage bars. At some point, this gave me the idea to do a small side experiment to test the idea that idea that risk increases nepotism.

To manipulate the perceived risks of helping, I created a novel “rescue” condition, where any donor vampire bat had to leave her warm, safe, dark, and comfy roosting location alongside her groupmates, then descend to an illuminated spot (vampire bats are very light phobic) where the trapped bat was stuck, and then to feed the trapped bat, she has to press her face to the cage bars (which sometimes makes her surroundings invisible) and regurgitate across cage bars. Compared to normal food-sharing, they don’t seem to like doing this. But they do it.

Sixteen of 29 bats were fed by others when trapped. They were fed by both kin and nonkin, but the degree of nonkin sharing declined quite obviously. All 15 starved bats that were tested in both trapped and free conditions received less food when trapped, and they received a consistently greater proportion of this food from closer relatives when trapped than when free. The vampires were more willing to feed mothers, daughters, and sons in the rescue condition. This is what we should expect if the bats’ nepotistic biases are exaggerated under dangerous conditions.

This paper was published in the journal Behavioral Ecology. Or if you lack institutional access you can get it from me here.



Posted in About cooperation, About vampire bats | Leave a comment

‘Team Vampire’ Fall 2016

Julia Vrtilek (Biology, Amherst College, 2015) is studying the development of grooming and food-sharing networks in young-of-the-year vampire bats.

What are your interests?
I find it fascinating and awe-inspiring that “from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” I’m interested in evolutionary biology, ecology, and animal behavior, as well as the latest thing I’ve read about in a recent cool article.

What do you hope to gain from working on the vampire bat project?
Primarily I hope to learn: about the bats, about research as a career, about myself. I’ve never worked with such a complex model organism before, and I know Gerry can teach me a lot about experimental design and statistics that I can use in my future work. I have mostly worked in microbiology, and the time has come to decide where I want to focus my future research. STRI is the perfect place for that; I am surrounded by smart, dedicated people who study all the things I’m interested in, and I hope to absorb enough about their work to help me concentrate my future efforts on my most enduring interests. I also hope to contribute to our understanding of reciprocity and cooperation!

What are your plans for the future?
This coming year, I expect to be working towards my Master’s degree in Zurich, and then I plan to proceed toward a doctoral degree.

Ellen Jacobs ( Ecology, Behavior, and Evolution, UC San Diego, 2016) is studying preference of young vampire bats for contact calls of mothers and other females.

What are your interests?
My primary interest is in animal social dynamics. I’m fascinated by the way that animals relate to each other, either in similar or totally different ways to humans. I’ve started focusing on acoustic communication, and I am very interested in the way that we can gain insight into the behaviors of different species based on their vocalizations. I am curious about the evolutionary and ecological causes and consequences of the ways that animals communicate. Ultimately, my interests are in understanding how different animals perceive and interact with the world and each other.


Julia and Ellen

What do you hope to gain from working on the vampire bat project?
The vampire bat project is a great way for me to explore my interests in communication and social dynamics, because vampire bats have such complex social interactions. I’m learning a lot about how researchers study social interactions, which I know will be useful in my future studies. I hope to gain experience in designing and running research projects, as well as statistical analysis that I haven’t had a lot of opportunities to do before. I’ve also never worked with terrestrial animals before, as much of my background is in marine biology, so I am finding the differences between terrestrial and marine animal research very interesting. STRI and the vampire bat project are a great introduction into the world of biological research, so I’m trying to soak up as much as I can.

What are your plans for the future?
I’m hoping to begin a Masters in the next school year, then a doctoral degree with the intention of pursuing a career in bioacoustics.

Rachel Crisp (currently MSc student at Exeter with Lauren Brent) is studying female social rank in vampire bats.

What are your interests?
From molluscs to mammals, sociality has arisen multiple times with varying degrees of complexity throughout the animal kingdom, and we observe social strategies that are both divergent or convergent. I’m interested in what influences the formation and structure of animal social networks, and what it can tell us about sociality in general. In addition, I’m interested in the influence of parasites, mating systems, and dispersal on social networks, and how sociality can influence cognitive abilities.

What do you hope to gain from working on the vampire bat project?
Vampire bats are interesting because they share some convergent social traits with primates despite diverging 66.5 million years ago. In primates, social rank is well described and is an important way that individuals balance the social benefits of group living against the social costs of escalating aggression. Currently we know very little about intra-sexual competition among female vampire bats and whether they resolve this social conflict in the same way as primates: by forming a dominance hierarchy. I’m hoping to gain insight into whether female vampire bats form a social rank and if rank is associated with grooming and food-sharing social networks. I hope this will elucidate some unexplained variation in vampire bat cooperation and give some insight into how vampire bat social networks compare to those of other socially complex vertebrates.



What are your plans for the future?
I’m particularly intrigued by convergent evolution in social systems and behavior across taxa. The social behavior of squid is a neglected area of study that I think could provide us with an interesting comparative study for social evolution. I’m also interested in using the variation in sociality among cephalopod orders to study social evolution. Ideally I would like to combine these (still rather vague) questions in some way.

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“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.

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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.

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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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