Primate Research in Barbados
May 3, 2012
A: The island of Barbados is the perfect location for studying primate behavior because it is the home of an ideal population of wild vervet monkeys (Ceropithecus aethiops sabaeus). The troop of vervets that we study has made the Barbados Wildlife Reserve a part of its home territory. Because the troop sleeps in the reserve at night but spends its days outside of the reserve, we know that we can observe the troop twice daily: as the monkeys leave the reserve around 6:30 a.m. and when they return to the reserve around 5 p.m. This degree of predictability is essential to conduct a field study within a three-week period. Another important factor is that the monkeys are habituated to the presence of humans. But what really makes these monkeys different from vervets found in other parts of the world is that the Barbados vervet population has been isolated from its natural predators for over 350 years. The African vervets from which our population descended have many predators: eagles, leopards, and snakes. They have evolved a complex alarm system by which each predator elicits a specific alarm call that in turn evokes a specific predator avoidance behavior from the monkeys in the area. Because the Barbadian vervets have lived without predatory pressure for so long, they can help us to answer questions about the nature (genes) vs. nurture (learning) of the African vervets unique alarm call system.
Q: Is the vervet your primary research subject? If not, what other subjects do you work with, and how does vervet research complement the other?
A: My primary research subjects are actually birds, not monkeys. When home at Centre, my students and I investigate the biological mechanisms that encourage breeding birds to return to their nest day after day. I “inherited” the Primate Research course from a retiring professor, Dr. Brent White, when I arrived at Centre several years ago. Although monkey research is unrelated to my bird research, it still falls within my broad area of interest: behavioral neuroscience.
Q: How do students first react to working with the vervets?
A: Prior to arriving in Barbados, I make sure my students have a healthy fear of the monkeys. They are wild, and hence unpredictable, animals with sharp canine teeth. We do everything we can to avoid an aggressive encounter with the monkeys and have been 100 percent successful in this respect. However, it is not uncommon to see tourists that are unfamiliar with the monkeys attempting to pet, poke—or even worse—pick up these wild animals. Monkeys are likely to bite as a result. So the student’s first reaction to the monkeys is one of respectful awe.
Q: Do you end up having students in the course who have previously studied doves with you? How do they find the experience?
A: It is not unusual for students who work in my lab to enroll in the primate research course. They find that it is necessary to have a lot more patience when conducting research in the field than in the lab. Our doves are always ready and available to be observed when the researcher finds it convenient to do so. The monkeys, however, are much less reliable. We spend many hours sitting quietly and waiting for them to enter the observation area. Sometimes they come one at a time over a three-hour period. Sometimes all 40 monkeys will come and go in less than 10 minutes. Sometimes they will show up three hours early, before we even arrive for our observations. And sometimes it rains. The monkeys aren’t active during rain—they stay in the trees and sleep. For every five observations periods, we probably get usable data from only three or four observations, despite our best efforts. This is pretty typical of all field research. The study progresses at the mercy of unpredictable subjects and unpredictable weather. On the upside, sitting quietly under a palm tree with nothing to do and nowhere to be for hours is a meditative experience—good for stress relief and mental well-being.
Q: The nature vs. nurture teachable moment sounds fascinating. Can you talk a bit more about how the vervet call system helps address this?
A: The African populations of vervets have a rather sophisticated alarm call system. When a monkey spots a leopard, the monkey makes a loud, barking alarm call. In response to this alarm, monkeys in the area will run into trees to escape the leopard. The vervets are much more agile in trees than are leopards so the monkeys are pretty safe there. If, on the other hand, a monkey sees an eagle, the monkey makes an acoustically different alarm call—a short double-syllable cough. When monkeys hear the “eagle alarm,” they look up in the air and/or run into bushes for protection from the eagle. Finally, the presence of a python will elicit a chutter, which sounds very different from the leopard and eagle calls. When they hear the chutter alarm, the vervets will stand up on their hind legs and look around in the grass. When they spot the snake, the troop will mob it.
Since first describing this unique alarm call system, researchers have questioned to what extent these alarm calls are learned and to what extent they are genetic. Within the framework of the classic nature vs. nurture debate, we would say that if the alarm call behavior was completely instinctive, babies are born ready to chutter when they see a snake and bark when they see a leopard, then “nature” is responsible for the behavior. In contrast, if this behavior must be learned by observing other monkeys making the appropriate alarm calls, then the behavior can be attributed to “nurture.” Many behaviors are a result of a combination of “nature” and “nurture,” or genetic and environmental factors.
Q: Are you able to distinguish one behavior from the other in your observations?
A: Within the African vervet populations, females that make the alarm calls give birth to babies that make the alarm calls as well. Because the babies both have their mom’s genes and are exposed to their mom’s alarm calls, it’s impossible to determine which mechanism leads to the alarm call behavior in the babies. The Barbados vervets have enjoyed a predator-free existence for over 350 years (about 12 generations). They haven’t had a need to make any of the three alarm calls and, therefore, they don’t. Since the alarm calls are not a part of the Barbados vervets’ common vocal repertoire, the vervet babies don’t have an opportunity to learn the alarm calls. If the alarm calls in the African population are acquired via learning mechanisms (nurture) then today’s Barbados population should not produce the correct alarm call in response to a leopard, eagle, or snake since they have neither seen any of these predators nor heard any of the alarm calls in their lifetimes. In contrast, if the alarm calls have a strong genetic influence, then we would make a different prediction. Even in the absence of predators, the gene(s) coding for the alarm call behavior will be passed from generation to generation. Therefore, you would expect that the current Barbados vervets would respond with the appropriate alarm call if they saw a leopard, eagle, or snake.
Q: Is this what your students have observed in previous research?
A: This is exactly what we found in 2011. One of the student research groups recorded the response of the vervets to a stick, a black rope, and a black rubber snake (all similar in length and diameter). The monkeys ignored the stick and the rope but made the chutter vocalization (snake alarm), bipedal stance, and mobbing behavior in response to the rubber snake. This is strong evidence for a genetic mechanism (nature). As I mentioned before, it is unlikely that genetics is the sole mechanism for this complex behavior. In Africa, young vervets make more alarm mistakes (e.g., giving the eagle alarm after spotting a leopard) than older vervets, suggesting that the alarm system is refined through learning and experience (nurture).
Q: Is this the type of research that will be carried on as part of your next CentreTerm trip?
A: When we return to Barbados in 2013, we plan to further test the alarm system. Do the Barbados vervets run into the bushes when they hear an eagle alarm and up into the trees when they hear a leopard alarm call? Will a model of an eagle elicit the double-syllable cough as it does in African vervets? We don’t know yet, but we are going to have fun finding out!
Interviewed by Michael P. Strysick, Director of Communications
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