37th meeting of the American Society of Primatologists (ASP): Poster Session

A PDF of my baboon handedness poster for this year's 37th meeting of the American Society of Primatologists (ASP) is now available on Academia.edu and ResearchGate. Thanks to those that stopped by my poster with valuable feedback and comments. 

ASP 2014: Decatur, GA

Good things come in threes: lemurs, monkeys, and apes; bacon, bacon, and bacon; ISBE, ABS, and ASP. In just a few days, I will be flying to Decatur, GA for the 37th meeting of the American Society of Primatologists (ASP). This will only be my second time attending ASP but I am already looking forward to meeting old friends and making new ones.

Traveling along with me will be my hamadryas baboon handedness poster, the same research I have presented at ISBE and ABS. Thanks for all the positive feedback and comments from both previous conferences. I have taken them into consideration and hopefully will present a much better poster at ASP. As always, I will have the PDF version of the poster up in this blog on the day of my poster presentation.

As per the current ASP conference schedule, my poster will be on Saturday, September 13th from 7 PM to 9 PM. That will be Session 1, and my poster is #75 (see abstract).

Also, of interest, is the Student Committee Meeting scheduled for Friday, September 12th at 3 PM in Avondale (room name). All students are invited to join us for this committee meeting and we are actively seeking students to participate in this committee. So, if you are a student that is attending ASP and is reading this. COME JOIN US!

See you all at ASP!

The Semantics of Vervet Monkey Alarm Calls: Part II - The Experiment

Last week, I blogged about the semantics of alarm calls in vervet monkeys. This post will focus solely on the ingenious experiment by Robert Seyfarth, Dorothy Cheney and Peter Marler (1980) to test whether vervet monkey alarm calls convey information or if these calls were just an uncontrollable auditory response to predators. Their question was simple. Would vervet monkey alarm calls alone elicit different responses?

A vervet monkey. Photo from Wikipedia.

Here's what the researchers did in the field. They used playbacks of recorded vervet monkey (subjects) alarm calls from concealed speakers. Equal amount of alarm calls for leopard, eagle and snake were used. These alarm calls were recorded from known adult male, adult female and juvenile vervet monkeys in the field. Trials were done when subjects were on the ground and also when they were in the trees. These trials were conducted in the absence of predators to eliminate visual cues from the caller.

Alarm calls were broadcasted in different amplitudes to mimic natural alarm calls. In succession from loudest to lowest amplitudes are alarm calls for leopard, eagle and snake. Subsequently, leopard calls have the lowest pitch while snake calls have the highest pitch. To control for the possible effects of amplitude, the researchers broadcasted alarm calls that do not differ significantly in the amplitudes for all three predators.

Table from Seyfarth et al. (1980). Click on illustration for its original size.

The alarm call playbacks showed two types of responses. First, subjects of any sex and age looked at the direction of the speaker and spent more time scanning their environment once an alarm call was made for more than 10 seconds. The researchers believe that they might be scanning for additional cues from the "caller" and the subject's surrounding.

Second, each alarm calls seem to elicit a distinct response from the subjects. Remember the trials were done when the subjects were on the ground and on the trees? When subjects were on ground, leopard calls were more likely to make them run up into the trees and eagle calls made them look up and run into cover (bushes) Snake calls made them look down. When subjects were on the trees, leopard calls were more likely to make them run higher in trees and to look down. Eagle calls made them look up and sometimes run out of trees. Snake calls made them look down.

From the results, Seyfarth et al. (1980) posit that vervet monkey alarm calls alone do elicit different responses. It's hard to tease out whether these alarm calls symbolize the predator "leopard" or a command "run up tree". However, we can postulate that these alarm calls are rudimentary semantic signals used to warn other conspecific of impending danger. For those that are not familiar with semantics, it refers to the meaning of a symbol, sign, word or phrase. In this case, vervet monkey alarm calls are semantic signals because it conveys a specific meaning.

Here's an interesting video by Robert Seyfarth summarizing his research with the vervet monkeys.

Reference:
Seyfarth, RM. Cheney, DL. Marler, P. 1980. Monkey responses to Three Different Alarm Calls: Evidence of Predator Classification and Semantic Communication. Science 210(4471): 801-803.

The Semantics of Vervet Monkey Alarm Calls: Part I

Anti-predatory alarm calls are important  for social animals to alert others of approaching predators. Without the presence of "language", some non-human primates are known to give out different predator-specific alarm calls to alert conspecific. These non-human primates include ring-tailed lemurs (Zuberbühler et al., 1999), white-faced capuchin monkeys (Fichtel et al., 2005), Diana monkeys (Zuberbühler, 1999), Campbell's monkeys (Ouattara et al., 2009) and vervet monkeys (Seyfarth et al., 1980).

Alarm calls are typically high frequency sounds because these calls are hard to localized by predators. On the other hand, low frequency sounds are easier to localized by predators. Calls that are hard to localized by predators are selected for because conspecific can pick up on the warning but predators cannot identify the location of the caller. If an individual successfully alert its social group of approaching predator yet does not reveal its location, it will significantly decrease the chance of the caller to be detected and increase the chance of its social group to avoid predation.

Vervet monkeys. Photo from Wikipedia.

Here, I will focus on the study of predatory alarm calls in vervet monkey (Chlorocebus pygerythrus) by Seyfarth et al. (1980) in the Amboseli National Park, Kenya. Vervet monkeys are Old World monkeys that range between Eastern and Southern Africa. These monkeys are diurnal and live in closely-knit social groups. They are quadrupedal and are both terrestrial and arboreal. Like all Old World monkeys, vervet monkeys have the characteristic cheek pouches that enables them to forage and store food to be eaten later. Male vervet monkeys have blue scrotal area and a red penis. Males and females are sexually dimorphic, with males slightly larger than females.

Male vervet monkey with blue scrotal area and red penis. Photo from Something Up Her Sleeve.

Vervet monkeys are known to elicit predator-specific alarm calls. Three well-documented vervet monkey alarm calls are those for leopard, martial eagle and python. Leopard alarm calls are short tonal calls produced in a series of inhalations and exhalations. Eagle alarm calls are low pitched grunt while python alarm calls are high pitched "chutters". Different alarm calls seem to evoke different responses to individuals that heard the alarm calls. However, the first reaction of a vervet monkey upon hearing an alarm call is to look at the direction of the caller. Looking at the direction of the caller gives them clues as to why the alarm calls were made and also where the caller is facing reveals the direction of the approaching predator. You can listen to these different alarm calls on this site.

As we said before, different alarm calls evoke different responses. Leopard alarm calls would make the monkeys run up into the tree to avoid being ambushed by the leopard. Also, these monkeys would sit on the branches further away from the tree because, even though leopards can climb trees, the branches could not support the leopard's weight. When an eagle alarm call is given, vervet monkeys would make them look up, run for the nearest bush or both to avoid an approaching aerial attack. Python alarm calls would the monkeys stand bipedally and look down on the ground.

A martial eagle. Photo by Jacques S G from Flickr.

Adult vervet monkeys are more discriminatory when eliciting alarm calls. Infants and juveniles calls however, are less discriminating as they attribute most terrestrial mammals with leopard calls, flying birds with eagle calls and stick-like figures with snake calls (although, compared to infants, juveniles are more discriminant when making alarm calls). In spite of that, adult vervet monkeys seem to elicit eagle alarm calls to different species of raptors and non-raptors (see illustration below). We can infer that adult vervet monkeys attribute eagle alarm calls to birds with the same silhouette as martial eagles. As vervet monkeys get older, they seem to have a better association between predator species and types of alarm calls. Vervet monkeys generally pay more attention to adult alarm calls than those of juveniles or infants.

Alarm calls made by infant, juvenile and adult vervet monkeys in response to sightings of birds of prey (raptors) and non-raptors. The number of calls cited for each age group refers to the total number of calls that were analysed (Gould & Gould, 1999). Click on illustration for larger view of the image.

The study of vervet monkey alarm calls by Seyfarth et al. (1980) laid an important ground work to better understand the complexity of animal communications. By showing that vervet monkeys make different alarm calls to different predatory species, we can posit that vervet monkeys have the ability to categorize different species. The ability to discriminate between terrestrial mammal, flying birds and snake-like objects starts during infancy in vervet monkeys. As they get older, they are better at associating predators with specific alarm calls.

An infant vervet monkey with its mother. Photo by Lip Kee from Flickr.

The ability to over generalize during infancy is evident in both vervet monkeys and humans. For example, upon learning the word "dog", human infants would refer to quadruped mammals they see as "dog". As the infant grows, so does the ability to associate the semantic meaning of words they learned. However, the acquisition of alarm calls in vervet monkeys is different than the acquisition of speech (language) in humans. Alarm calls in vervet monkeys are instinctual and not learned. Humans, however, have to learn their language. Failing to do so during the "critical period" generally will result in the inability to learn language in later years. Feral child are examples of human infants that lack linguistic input during their critical period of language acquisition.

Most of us interpret animal alarm calls as an uncontrollable auditory response to fear or pain, akin to humans yelping if we had our finger caught in a door. While this is not entirely false, some animal calls actually convey information from the caller to the listener. Seyfarth et al. (1980) posit that vervet monkey alarm calls are actually basic semantic signals or symbolic signals because each alarm calls seem to mean something to these vervet monkeys. While we don't know if these alarm calls actually mean "leopard" or "run up to the tree", we do know that it conveys specific information to their conspecific about approaching predators.

I will be blogging Part II of this post later this week, where I will explain in details the experiments done by Seyfarth and Cheney on vervet monkey alarm calls.

References:
Cawthon Lang KA. 2006 January 3. Primate Factsheets: Vervet (Chlorocebus) Taxonomy, Morphology, & Ecology. http://pin.primate.wisc.edu/factsheets/entry/vervet. Accessed 2011 March 9.

Fichtel, C. Perry, S. Gros-Louis, J. 2005. Alarm calls of white-faced capuchin monkeys: an acoustic analysis. Animal Behaviour 70(1): 165-176. doi: 10.1016/j.anbehav.2004.09.020.

Gould, JL. Gould, CG. 1999. The Animal Mind. Scientific American Library.

Ouattara, K. Lemasson, A. Zuberbühler, K. 2009. Campbell's Monkeys Use Affixation to Alter Call Meaning. PLoS ONE 4(11). doi:10.1371/journal.pone.0007808.

Seyfarth, RM. Cheney, DL. Marler, P. 1980. Monkey responses to Three Different Alarm Calls: Evidence of Predator Classification and Semantic Communication. Science 210(4471): 801-803.

Zuberbühler, K. Jenny, D. Bshary, R. 1999. The Predator Deterrence Function of Primate Alarm Calls. Ethology 105: 477–490. doi: 10.1046/j.1439-0310.1999.00396.x.

Zuberbuhler, K. 2000. Referential labelling in Diana monkeys. Animal Behaviour 59(5): 917-927. doi: 10.1006/anbe.1999.1317.