Many species are known to produce alarm calls in response to predators or other perceived threats. There are a variety of questions and hypotheses about the purposes of these signals, how they evolved, and the ways in which calls can vary within species. For example, did signals evolve to scare away predators or to warn other members of a group? Or are they simply a response to the distress caused by the predator? Can different threats elicit different response signals? If so, how and why do they differ?
In the paper “Predator-deterring alarm call sequences in Guereza colobus monkeys are meaningful to conspecifics,” Anne Marijke Schel, Agnes Candiotti and Klaus Zerberbuhler discuss the alarm calls of Guereza monkeys. Two main predators of Guereza monkeys are leopards and crowned eagles. The calls of each of these species result in different responses from Guereza monkeys. For example, when they hear an eagle shriek, the monkeys are more likely to look towards the sky than when they hear a leopard roar. In addition, different alarm calls are produced in response to the leopard than to the eagle. Guereza monkey alarm calls consist of sequences of roars. When responding to leopard roars, monkeys produce a large number of short roaring sequences while when responding to eagle shrieks, they produce a small number of long roaring sequences. There are two hypotheses regarding the difference between these two alarm signals; it could be the result of different levels of threat or it could be a way of telling other monkeys what type of predator is coming. The fact that monkeys are able to recognize the difference between the two alarm calls and respond to alarm calls in similar ways to which they respond to the calls of the predators indicates that the two different calls contain real and useable information about what type of threat is present.
Schel, Candiotti and Zuberbuhler concluded that the alarm call of the Guereza monkey has two main purposes. The first is to chase predators away and the second is to communicate danger to other monkeys. The fact that alarm calls for leopards and eagles are different is helpful in both of these contexts. The alarm call in response to the eagle is more threatening and this makes sense because Guereza monkeys try to chase eagles away more often than they try to chase away leopards. In addition, the difference between the calls lets other monkeys know what type of danger is present.
-Lauren Lynch
That’s really cool! I wonder how many calls in total they have for predators. Also, it would be interesting to try to figure out the extent to which calls are learned as opposed to innate. Would young monkeys be able to understand the alarm calls?
ReplyDeletePosted by Katie Kalutkiewicz
My best guess on why each call is established the way it is because of the locomotion abilities of the two different predators. With a leopard, the short roars but long sequence is because a leopard is typically going to be on the ground when the monkeys see it; opposed to the eagle in which it can dive bomb into the tops of the trees where the monkeys are at and cover about 60ft in a matter of seconds.
ReplyDeleteI feel that the calls have developed into what the monkeys can hear and get ready for in the tree tops. With an eagle a quick distinguishable call needs to be made, and with a leopard, a call that is going to be heard more from monkey to monkey in the depths of the jungle needs to be able to transmit from monkey to monkey clearly; and there's just simply more noise under the tree tops.
-Peter Lucas
I wonder if other intra-specific calls display this level of information. For instance, if the monkeys are communicating that food can be found in a place, do their communications vary depending on where the food is, or what the food is, so that other monkeys can find it more efficiently?
ReplyDeleteThis sort of communication would be selected for much more lightly (since the consequences of not communicating about predators are more dire than communicating about food) so if they WERE communicating that sort of low-priority information, it might be a clue as to how far on the evolutionary track toward truly complicated verbal language they've progressed.
-Alice Trei
Do you know what the response to the threat calls are? It would be interesting to compare the reactions of the other monkeys to the different calls. Do you know if there is a separate call that is used for all of the other predators? Or do they use the two calls for all avian predators and all land predators?
ReplyDeletePosted by: Sara Weaver
I've heard of other animal species that have predator-specific alarm calls as well, but I've never thought of alarm calls as functioning to scare predators off as well. I wonder how often it actually works, or if many monkeys producing the call at once has a greater effect.
ReplyDelete-Jane de Verges
It would be interesting to see if the monkeys would create a new alarm call if a new type of predator was introduced into their environment.
ReplyDeleteCharles Carville
It would be interesting to observe instances when these alarm calls were being made and comparing them to alarm calls in response to other stimuli. How do you believe these calls originate in the development process of these monkeys? And do you think it is possible that the weaker alarm call (leopard) may be used in child rearing and teaching the younger monkeys about possible threats in the environment?
ReplyDelete-Himanshu Shah