Red-Eyed Rump Shaker

A photo of a red-eyed treefrog taken
by Carey James Balboa at Wikimedia.

At night, male red-eyed treefrogs gather on saplings over Central American forest ponds to show off their stuff for the ladies, producing self-advertising “chack” calls. Despite the fact that they gather in groups, they defend their calling territories from flirtatious male competition. Females assess the available males and usually mate with a single male, who mounts her and clings on for dear life in a behavior called amplexus until she lays eggs that he then fertilizes. Occasionally, multiple males will try to mate with the same female at the same time, which usually results in two ticked-off male frogs.

What does an angry red-eyed treefrog do, you may ask? A mildly irritated treefrog will likely produce territorial “chuckle” calls, to let rivals know this is his favorite calling-plant and they’d better step-off. But a really ticked-off red-eyed treefrog rapidly lifts and lowers his hind end in a behavior called tremulation.

 
"Step off, I'm doing the hump!" Video by Michael Caldwell.

 Not much is known about this tremulation behavior. Is it something they do just to release anxiety or is it a communication signal? If it is a communication signal, is it a visual signal or a vibrational signal or both? And what exactly might it communicate?

Michael Caldwell, Karen Warkentin and Gregory McDaniel from Boston University, and Gregory Johnston from Flinders University in Australia, set out to ask the red-eyed treefrog if the tremulations were a communication signal and what they may mean. But without Dr. Doolittle’s powers of talking to the animals, how can scientists determine what and how animals are communicating?

First, the researchers observed natural interactions between males at choruses in the wild and recorded everything they did. They found that male red-eyed treefrogs will often approach another male while making “chuckles” and “chacks”. These males also tremulated in every aggressive interaction observed. Some of these males kicked with their back legs and some encounters even escalated to wrestling. Eventually (usually anywhere from a minute to an hour later, but occasionally several hours later), one of the males would submit by fleeing the plant or remaining silent and motionless. The dominant male would then resume his self-advertising “chack” calls. So males use tremulation in aggressive contexts with other males, but does that mean that it is a signal?

Males that won encounters tremulated more and used more
"chack" and "chuckle" calls than did males that lost encounters.
Figure from Caldwell et al. 2010 Current Biology paper.

The researchers then conducted staged contests by placing pairs of calling males on the same sapling. In these staged contests, males showed all the same aggressive behaviors the researchers had observed in natural conditions, and most ended in a wrestling match. The males that won their encounter produced more calls and more tremulations than did males that lost their encounter (Check out the graph above). So tremulations are used in the context of aggression with other males and winners tremulate more than losers. It looks like these tremulations are an aggressive communication signal, but to know for sure, we need to know if other males respond to them. And are tremulations a visual signal, a vibrational signal, or both?

So the researchers had to get creative and take it one step further: They put a robotic frog on a vibrating shaker that could mimic the visual display of a tremulation. They attached a separate vibrating shaker to the plant to mimic the vibrations of a tremulation. Now, they could look at the effects of the visual and vibrational components of the tremulation behavior separately!



Robofrog! Notice the jointed limbs and the metal rod sticking out of the robot's
belly. That rod is connected to a shaker that moves the robot so it looks like
he is performing a tremulation display. A separate shaker is connected to the
sapling to send the vibrational component of the display. This way, the
researchers can expose frogs to the visual component and the vibrational
component of the tremulation display separately. Photo by Michael Caldwell.

The researchers compared male red-eyed treefrogs that were exposed to (1) nothing, (2) a frog robot that does nothing, (3) a frog robot that “tremulates” with both plant vibrations and visible movement, (4) “tremulation” vibrations in the plant, without the frog robot, (5) a frog robot that moves it’s butt up and down but doesn’t produce vibrations, and (6) white noise vibrations in the plant (this is just a generic vibration).

Males responded aggressively to the imitated tremulation vibrations, visual or combined but not to any of the other treatments. This suggests that tremulations are a communication signal that rival males respond to. Interestingly, males only tremulated in response to tremulation vibrations. This suggests that the vibrational component is important to sending the full aggressive signal.

Males have aggressive responses to the visual display alone,
the vibration alone, and the visual display combined with the
vibration. But males only tremulated in response to vibrational
signals. Figure from Caldwell et al. 2010 Current Biology paper.

The sensitivity to soundless surface vibrations is widespread among animals, but we know very little about vibrational communication, especially in vertebrates. Michael, Gregory, Gregory and Karen have cleverly shown us that male red-eyed treefrogs use vibrational signals in contests with each other. How many other species will we discover using this silent channel of communication if we just listen?

Want to know more? Check this out:

Caldwell MS, Johnston GR, McDaniel JG, & Warkentin KM (2010). Vibrational signaling in the agonistic interactions of red-eyed treefrogs. Current biology : CB, 20 (11), 1012-7 PMID: 20493702

Where the Wild Things Are: Amazing Animal Watching Vacations Part 4

Wouldn't you rather be here right now?
Photo by RAMDOM X at Wikimedia

Need to get away? Want to go somewhere that is both adventurous and relaxing, exotic yet relatively easy to get to? Want to see monkeys, dolphins, toucans, and iguanas in the wild? Imagine a place with long sandy beaches, a mountain view, a tropical rainforest and so many wild animals you’ll forget you’re not at a zoo... until you realize how close they really are. That place actually exists, and it is Manuel Antonio National Park in Costa Rica.

Manuel Antonio is Costa Rica’s most visited national park, and for good reason. Located on the Pacific Coast of Costa Rica, the park includes 682 hectares of beautiful beaches and lush rainforest laced with maintained trails as well as a large protected ocean reserve. It is relatively easy to get to (more on travel below) and there are a number of hotels within walking distance of the beach and park entrance.

Coatis are close relatives of raccoons, and like
raccoons, they can be pretty bold if they think
you might have food. Photo by Matt Magolan.

These white-faced capuchins are plotting to
take your snacks. Photo by Matt Magolan.

If you love animals (and if you’re reading this, I know you do), you will find yourself in a wild wonderland. White-faced capuchins run along the branches and squirrel monkeys leap through the air. Howler monkeys and countless colorful songbirds chorus in the mornings. You can search for sloths and iguanas in the trees. You can even see animals you may not have heard of, like agoutis and coatis. You can see all these animals and more from amazingly close-up. But whatever you do, don’t try to touch or feed the animals – Many of them (the white-faced capuchins in particular) have become very bold and may aggressively steal your food. A friend of mine had a granola bar grabbed right from her hand by an angry little capuchin – I don’t think she ever felt quite the same about monkeys after that.


Manuel Antonio National Park is one of the few
places in the world where you can still see an
endangered squirrel monkey. Photo by
Matt Magolan.

There are also efforts underway to responsibly manage the ecosystems of the Manuel Antonio region. The National Park limits the number of park visitors to no more than 600 per day on weekdays and 800 per day on weekends. Also, conservation projects such as the Titi Conservation Alliance and Saving Mono Tití are working hard to preserve the habitats necessary for the survival of the vulnerable squirrel monkey (mono tití in Spanish). Both of these groups are working hard to plant tens of thousands of native Costa Rican trees from Manuel Antonio eastward, where small populations of squirrel monkeys are isolated from one another by palm plantations and large resorts. When the total population of squirrel monkeys in the Manuel Antonio area is estimated under 2,000 individuals, maintaining group contact is critical to preventing inbreeding. Despite the considerable efforts and successes of groups like these, development, hunting and the pet trade still threaten this species.

Travel to Manuel Antonio is relatively simple (as international travel goes). Once you make it to San José, the capital city of Costa Rica, you can either hop on a 20 minute flight by Sansa Airlines or a 3.5 hour bus ride from the Coca Cola bus terminal. If you are feeling even more adventurous, you can rent a car to drive yourself, but be prepared to get lost, drive difficult terrain (make sure to get a 4X4) and navigate some of the most ruthless traffic you’ll ever drive in. Comparatively, the plush, air-conditioned bus is much more relaxing.

So if you are looking for a vacation idea, Manuel Antonio, Costa Rica is an animal lover’s paradise. For more information or to plan your own trip, check out some of these resources:

1) The official Manuel Antonio website
2) Go Visit Costa Rica
3) Lonely Planet
4) The Lonely Planet Costa Rica travel guide

Don’t Challenge a Fruit-Eating Bat to a Drinking Contest

Did you think humans invented inebriation? Guess again!

Frugivores (animals that eat fruit) and nectarivores (animals that eat nectar) are limited to food sources that last a relatively short time before they ripen, then ferment, then completely rot. So you would think that a fruit-eating animal would be much more successful at feeding itself if it could eat foods in various stages of fermentation, right? Not only would the ability to eat fermented fruits increase food abundance, but alcohol also has high caloric content (ehem: beer bellies), and makes the food easier to find by that distinctive alchy-smell. So rock on, little frugivores! It’s all good!

Watch this drunk squirrel try to escape the

"predator"-people with the camera. You're welcome.



Or is it? Imagine you’re drunk: kinda happy, stumbling occasionally, saying things you’ll likely regret in the morning, and getting lost on the way to the bathroom. Now imagine you’re being chased by a mountain lion. Crikey! You were so busy getting blitzed on fermented fruit, you forgot that you are a prey animal… and it’s a dangerous world out there!

If frugivores, such as fruit-eating bats, consumed a lot of fermented fruit, you would think they would be drunk all the time and would fly wonky and get lost and generally be less likely to survive… unless they had developed an ability to tolerate alcohol. Dara Orbach, Nina Veselka, Louis Lazure and Brock Fenton at the University of Western Ontario and Yvonne Dzal at the University of Regina decided to test the ability of several fruit-eating bats to hold their liquor. The researchers went to Belize and caught bats from six different fruit-eating species. They fed them either sugar-water or sugar-water with 1.5% alcohol in it (that’s less than a Molson Light) and later measured their blood alcohol level (BAC) in their saliva.

A little yellow-shouldered bat being fed it's alcoholic cocktail.
Photo provided by Nina Veselka.

Then the researchers put the bats in an obstacle course. That’s right, an obstacle course! They timed how long it took each bat to traverse the obstacle course (if they completed it) and counted how many times they ran into something or went in a circle. Afterwards, they gave them time to sober up before they released them back into the wild… presumably to go tell their friends about the crazy night they had. Ooohhh, was this gonna be funny!

Scientists building the drunk-bat obstacle course in Lamanai, Belize.
Photo provided by Nina Veselka.

To the researchers’ surprise, despite the fact that several bats had a BAC over 0.3% (the equivalent to a 150 pound person after 10 drinks), the bats on alcohol did not seem to be impaired in any way! They traversed the obstacle course just as fast and completed the course just as often as their kiddie-cocktail sugar-water drinking counterparts. They never even ran into anything.

So, I guess we’re not going to be entertained by drunken bat antics. But this is good news for the fruit-eating bats – Somehow, they are able to metabolize fermented fruit to get the caloric benefit without the risks of impairment. Now, if we could just figure out how they do that…

The moral of this story: Don’t drink alcohol when there are predators around unless you are a fruit-eating bat. And don’t challenge a fruit-eating bat to a drinking contest. He will drink you under the table!

Want to know more? Check this out:

Orbach DN, Veselka N, Dzal Y, Lazure L, & Fenton MB (2010). Drinking and flying: does alcohol consumption affect the flight and echolocation performance of phyllostomid bats? PloS one, 5 (2) PMID: 20126552

Staying Safe While Working With Wild Animals

On Thursday June 28, Andrew Oberle, a primatology graduate student from the University of Texas at San Antonio, was viciously attacked by chimpanzees while giving a tour at the Jane Goodall Institute Chimpanzee Eden Sanctuary, a chimpanzee rescue center in eastern South Africa. According to the Associated Press, Andrew crossed between two safety fences that separated the chimps from the tourists in order to retrieve a rock that the chimps would use to throw at tourists. It was then that two chimps grabbed Andrew’s feet and pulled him under the inner electric fence, biting him severely and dragging him for nearly a kilometer (half a mile). The sanctuary director fired two shots into the air to scare the chimps away from Andrew, but by that point, he had already sustained many severe injuries, including fractures and the loss of fingers and part of an ear. (CNN reports slightly different details).

Andrew Oberle at the Jane Goodall Institute Chimpanzee Eden Sanctuary.
Photo from the HelpAndrewOberle Facebook page.

Andrew’s mom, Mary Flint, said her son has been passionate about chimps since the seventh grade. Andrew knew the risks involved in working with primates in general and especially with chimpanzees with a history of abuse, but that was not enough to prevent this horrific accident. There are many of us, like Andrew, that are passionate, adventurous and curious enough to pursue careers working with wild animals. I asked our community of field biologists, lab animal researchers, zoo and aquarium workers, wildlife rehabilitators, wildlife guides and educators, animal trainers and veterinarians for stories and advice on how we can do what we love and stay safe doing it. The responses poured in. Here are some of our lessons and stories:


Know your animals.

This includes knowing the natural history and behaviors of the species you will be interacting with, training in and using appropriate precautions (safety gloves?), and recognizing and responding effectively to threat or fear indicators. Know what stimuli your animals are particularly sensitive to. A journalist on a photography safari in Tanzania cut his head on a timber beam in camp. The next day, their driver inched their Land Cruiser up to a group of lionesses for a photograph when one of the lionesses began to approach the vehicle while sniffing the air, likely following the blood scent. This group was smart enough to give up the photo opportunity and drive away.

You also need to know the specific population or individual animals you will work with. Are they hungry or well-fed? Do they have experience with humans? Researchers working with American alligators note that populations that have been fed by humans are much more dangerous than those that have no human experience. This is true of many other species as well. Were the animals abused? Do they have a history of aggression or anxiety? In the case of the chimpanzees at the Jane Goodall Institute Chimpanzee Eden Sanctuary, many of them have been rescued from abusive situations and have abnormally high levels of fear and aggression as a result.

If you can read the animals you are working with, you will be better able to avoid postures they may perceive as threatening (such as approaching them directly or with quick motions, using eye contact, and showing your teeth). Hopefully this will help prevent a dangerous animal reaction, but will also help you to prepare if an animal does attack.


Give them space.

Most animals have a comfort zone, just like we do. If you get in their personal space, they are likely to feel threatened. Sometimes we get in an animal’s comfort zone on purpose because it is part of the job, and this is when training and protective gear is vital. Even more dangerous is when we unknowingly get in an animal’s comfort zone and provoke a startle response in everyone involved. One wildlife guide did not realize how close he had gotten to some elephants standing behind bushes. They were apparently caught off-guard too and responded by chasing him to his car… and then after his car! But these surprises can happen closer to home too. In the field I always check my boots before I put them on: You never know what snake, scorpion, or spider may have snuggled into them for the night. But I often forgot to check my clothes. That changed after a tarantula crawled out of my pants leg while I was walking to work! A local later identified the tarantula as a “matacaballo” or “horse-killer”. Be aware of your surroundings and never put your clothes or boots on without checking them first.

Wild animals are a lot more likely to flee than attack when given the space to do so. For this reason, be especially cautious of animals in captivity and don’t corner an animal without the appropriate training and equipment. Don’t keep trying to get closer for a better picture if the animal seems wary of you. And no matter how tempting, don’t push a mother with cubs to get a better picture. One wildlife photographer was graciously spared by an angry tigress, but another photographer shooting a hippo with her baby was not as lucky.


Respect them – They are smarter, stronger, and faster than you think.

One researcher recalled a time that he was working with a restrained pigtailed macaque in the lab. A technician, rocking the lab-necktie, was entertaining himself by leaning over and pestering the monkey. Suddenly, the monkey grabbed his necktie, pulled his face closer, reached down with its other hand to pick up a pile of poo, and smeared it on the pesty technician’s face. The wise monkey’s advice here: Don’t. Just, don’t.

And on a similar note, even cute, cuddly-looking baby owls (and other species) can bite and scratch the bejeezus out of you. Don’t let your guard down when handling baby wild animals just because they’re adorable.


Remember that animals are not the greatest risk in the field… Not by a longshot.

Photo by Paul Downey at the UK Ministry of Works
on Wikimedia Commons.

Despite the collection of animal hazards listed here, it is important to keep in mind that the vast majority of injuries in the field are not caused by the animals being studied, but rather by natural hazards, parasites, and people. Usually our own clumsiness and carelessness are our downfall, but sometimes we fall victim to bad drivers (including ourselves), thieves or violent people. As one researcher said, “Active aggression tends to come from conspecifics”. Get your preventative medical care, learn to drive stick (and perhaps take a defensive driving course), bring a first-aid kit and water (and water-purification system and bug net if needed), wear appropriate clothes to protect against insects and weather, know the local currents if you plan to swim, educate yourself about the customs and processes of where you are going, and remain aware and thoughtful when you are in the field.

By Sunday, Andrew’s condition had stabilized and he was moved from critical condition to intensive care. He has now undergone two surgeries and remains sedated. If you would like to leave a message of support for Andrew and his family, his friends have set up a Facebook page. If you would like to donate to Andrew’s medical costs and his family’s travel expenses, you can donate here. And if you would like to learn about and donate to the Thin Green Line, an organization that supports Park Rangers in developing nations and conflict zones, go here.

Thanks to everyone who contributed stories and advice for this piece: Stephen Ambrose, Ian Batterman, Al Beck, Devendra Bhardwaj, Dennis Owusu Boateng, Sam Bryks, Denise Donovan, Carrie Duafala, David Gaines, Jerry Haigh, Caleb Hickman, Pat Hoy, Denis Lane, Lisa Langell, Tom Larimer, Jacqueline Levine, David Manning, Bery Pannkuk, Rob Parkin, Sabyasachi Patra, John Pemberton, Steve Phelps, Kath Potgieter, Brad Rence, David Sinn, John Taylor, Ann Turner, Veronika Valdova, Joep van de Vlasakker, Armonía Vega Quintero, and Menno Witteveen.

Steroids Won't Help If You're a Loser

The more we study physiology and behavior across groups of animals, the more we find we have in common in the types of behaviors we express and the biological machinery of how our bodies influence what behaviors are expressed and when. But similarity does not mean the same. Sometimes seemingly small physiological differences can have big behavioral consequences.

A snuggly California mouse pair.
Photo from the Marler lab.

A lone wire-walking white-footed mouse.
Photo by the National Park Service.

Take the California mouse and the white-footed mouse, for example. Both are small grayish to brownish species of North American deer mice (the Peromyscus genus). But behaviorally, these species are quite different. One noticeable difference in their behavior is that California mice are very territorial and dominant towards intruders, whereas white-footed mice are more welcoming of other mice (or at least more ambivalent to their presence). These species also differ in how they respond to dominance challenges: California mice that win a challenge (by getting their opponent to show submissive behavior) are more likely to win future challenges (this phenomenon is called the Winner Effect). However, white-footed mice have the same probability of winning or losing a challenge regardless of whether they won or lost the previous one. Interestingly, the experience of winning causes the levels of testosterone (a steroid hormone) to surge in California mice, but not in white-footed mice. Could this difference in testosterone explain this difference in behavior between these two species?

Cathy Marler and her colleagues at the University of Wisconsin at Madison recently explored this question. They compared four groups of male mice: (1) California mice that won three challenges and had a saline injection after each win, (2) white-footed mice that won three challenges and had a testosterone injection after each win, (3) white-footed mice that won three challenges and had a saline (without hormone) injection after each win, and (4) white-footed mice that were handled by researchers three times (and had no dominance challenges) and had a testosterone injection after each time they were handled. Then they placed each mouse with a new challenger and measured what percentage of males in each group were dominant versus subordinate.


Most California mouse males that have been previously dominant and had
no hormone treatment win a future dominance challenge (black bar).
White-footed mice (grey bars) are only likely to win their next dominance challenge
if they had previously won AND had additional testosterone (W+T), but not if they
won without added testosterone (W+S) or had testosterone without wins (H+T).
Figure from Fuxjager et al., 2011, Proc. R. Soc. B.

Marler and her colleagues found that similar to the natural state, white-footed mice that won three times and were not injected with testosterone were less likely to win a later challenge than California mice that also won three times and were not injected with testosterone. But, white-footed mice that won three times and were injected with testosterone won their next challenge as often as the California mice did! Presumably, the California mice had their own natural surge of testosterone whenever they had a winning experience and the testosterone injections given to the white-footed mice after their wins mimicked this effect and increased their odds of winning later.

However, testosterone injections alone were not enough to increase the chances of winning: the white-footed mice that had testosterone injections without winning challenges were just as likely to lose their next challenge as those that had saline injections and won previous challenges. It’s the combination of winning experience paired with a surge of testosterone that is the winning formula. You can think of it this way: When (fictional) scientists gave frail Steve Rogers "Super Soldier Serum" to turn him into Captain America, it only worked because Steve Rogers was already a winner at heart. Had they given the serum to someone less remarkable, Michael Cera, for example, they just would have ended up with this:

Michael Cera's attempt to be Captain America. Photo by Gage Skidmore.

So what does this all mean? For one thing, it appears that white-footed mice have all of the necessary brain-wiring to show a Winner Effect in the same way that California mice do, but they don’t produce the testosterone surge to activate it. This opens up a bunch of new questions, like: Why don’t white-footed mice have a testosterone surge after winning? Is there some aspect of their lifestyle that would make such a testosterone surge costly? How does the body know to release testosterone in response to a social experience anyway? Other than testosterone, what makes a winner a winner?

In the end, the experience of winning is critical to the Winner Effect: Testosterone alone won’t help you win your next challenge. So don’t think steroids are gonna help you if you suck at your sport of choice. You have to already be a winner for extra testosterone to help you win… and at that point, who needs it?

Want to know more? Check these out:

1. Fuxjager MJ, Montgomery JL, & Marler CA (2011). Species differences in the winner effect disappear in response to post-victory testosterone manipulations. Proceedings. Biological sciences / The Royal Society, 278 (1724), 3497-503 PMID: 21490015

2. Oyegbile TO, & Marler CA (2005). Winning fights elevates testosterone levels in California mice and enhances future ability to win fights. Hormones and behavior, 48 (3), 259-67 PMID: 15979073