CONTINUING EDUCATION
Special Topic: Extern Mary Catherine
Chapter 8: Communication in Spider monkeys:
The function and mechanisms underlying the use of the whinny
Spider monkeys have a unique and fascinating vocal communication repertoire. Current research is exploring the vocalizations of spider monkeys in hopes of understanding what kind of information is communicated in their calls. As canopy dwellers, spider monkeys travel great distances through a complex environment in search of fruit patches. In order to communicate through the dense canopy, spider monkeys employ long-distance vocalizations as a means to locate group members, food, and avoid danger.
Spider monkeys have a fission-fusion society, meaning their social groups fracture into smaller subgroups (or even just individuals) and disperse throughout their environment to forage for food but join together again in the evening. Fission-fusion societies are found in animals with complex cognitive abilities related to building and maintaining social relationships. For example, dolphins, elephants, and chimpanzees all have fission-fusion social systems as well. Spider monkey communication is thus very intricate and we are still trying to understand the information conveyed in their calls.
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| Carlos often whinnies when eating his favorite treats! |
Current research suggests two vocalizations of spider monkeys, the trill and the whinny, may contain information on the animal making the call. Whinnies appear to act as a food call, increasing in frequency when there is an abundance of food. Researchers suggest this may act as a way to let other group members know where food is available and possibly to lower predation risk through safety in numbers. Members of a subgroup often stay an average of 30 meters apart from one another while they disperse and forage, while different subgroups keep a distance of 170 – 370 meters from one another. Though they may be visually separated from other members of their group, a spider monkey whinny can be heard from 300 meters away in a typical habitat!
However, the whinny is not just a sound to alert conspecifics about food. The acoustic structure of whinnies has many variations that are thought to contain specific information on both the identity of the caller and the identity of the intended recipient. This allows spider monkeys to stay in contact with specific individuals throughout their day. Trill vocalizations are also thought to contain information about the identity of the caller. In fact, studies show slight variations in the auditory make-up of a call represent identities of each group member. In other words, these calls may act as labels in how they address each other… something similar to having names! Doesn’t it make you wonder what kind of whinnies Carlos and Montana have for each of us?
-Campbell, Christina J. Spider Monkeys: The Biology, Behavior, and Ecology of the Genus Ateles (Cambridge Studies in Biological and Evolutionary Anthropology). UK. Cambridge University Press. 2008.
Special Topic: Intern Simon
The ecology of the pygmy marmoset, Cebuella pygmaea: some comparisons with two sympatric tamarins; by Pekka Soini
Introduction
The word “sympatric” refers to different species that occupy the same geographic area. In this chapter the author focuses on pygmy marmosets—a species previously housed at PPS—and compares them with two other monkeys: the moustached tamarin and the saddle-back tamarin. PPS currently provides refuge for two saddleback tamarins: Gaia and Galatea. After a brief description of the pygmy marmoset, we will see how they coexist with the two tamarin species.
Description and Ecology of the Pygmy Marmoset
You can find pygmy marmosets in the upper Amazon lowland forests of Peru. As their name suggests, they are tiny. The average weight for an adult is 119 grams: less than the weight of the average hamster. They live in groups that range in size from 2-9, but on average a troop consists of about five individuals—typically one reproductive female, her mate, and their offspring. Even in cases where there are more than one adult female, only one will be reproductively active. When children become young adults they leave in search of a mate of their own. But new births—usually to twins—constantly occur every 5-7 months, replacing those who leave.
Pygmy marmosets are habitat specialists. They live in floodplain forests along rivers. They are nomads who prefer to stay put for as long as possible. Troops occupy a range of about half a hectare, but the actual size of a home range depends on the distance between the gum trees and vines that these monkeys depend on for food. They will find a tree that can support the group and vampire-ize it until it no longer produces enough sustenance to sustain the group, at which point it is time for the troop to uproot and find another food source. But until the tree has been sapped of its sap—which can take a few months to several years—the troop will make that tree their central territory, and most social interactions will play out around this home base.
Comparing the Pygmy Marmoset to Their Sympatric Relatives
While pygmy marmosets are highly specialized, their two larger tamarin brethren—the saddleback and the moustached tamarins—live a very different lifestyle. Rather than living on gums and saps, they have a more generalized diet of fruit and insects and will only eat gum or sap rarely as a dietary supplement when fruit is scarce. Though the pygmies have a small home range, the members of the group tend to spread out within that range, often foraging individually. In contrast, the two tamarin species have a much larger range—a consequence of relying on the availability of fruit—but will stick close together when on the search for food. Furthermore, for the tamarins their home range may be larger than the pygmy’s but it does not change. They are well aware of where the fruit trees are and when a given tree is producing ripe fruit. They perpetually make the rounds to where the ripe fruit is, knowing that when one tree has been exhausted they can return to it when it is replenished. In this way, they never have to leave the parameters of their home range. For the pygmy marmosets, when a tree has been exhausted they abandon it and will change their home range several times in a troop’s lifetime.
Saddlebacks are nearly three times the body mass of a pygmy marmoset and the moustached tamarin is nearly four and a half times larger. This has reproductive ramifications. The pygmy marmoset’s small size and reliance on a food source that is more stable than fruit allows them to produce offspring at a faster rate than the two tamarins. They are able to give birth every six months while saddlebacks take eight months and moustached tamarins take anywhere from eleven to twenty months. The smaller size of the marmosets also means that they can effectively occupy a smaller home range. The pygmies occupy a mere ½ a hectare, while saddle-backs have a home range of 16 hectares, and the larger moustached tamarins: 25 to 35 hectares.
Conclusion
As we can see, diet, body mass, and ranging patterns all inter-relate to one another and comprise the strategy that a species employs to be successful. Though all three of the aforementioned species are primate, each has adapted to its own unique niche so that they can all coexist in the some habitat. This helps support a stable ecological system.
-Rylands, A.B. Marmosets and Tamarins. Systematics, Behavior, and Ecology. Oxford, U.K.: Oxford University Press, 1993.
Special Topic: Intern Olivia Brown
The Capuchin Body
This chapter discussed the morphology of the Capuchin body and how it helps them function in the wild. The White-faced Capuchins, the species living at PPS, have pale skin on their faces that may darken with age. They also have black tails. Capuchins weigh about 2.7 kilograms, in the middle of the size range of neotropical primates.
The Capuchins’ hands, teeth, tail, and eyes function well with their large brain to body size to make them a successful species.
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| Viola uses her hands and teeth to get the sweet juice from sugar cane |
Capuchins have a much larger brain to body size than that of other New World primates. It is more on the scale of old world monkeys. Capuchins use their large brains to forage for hard to find foods, they are omnivores but eat insects and difficult to get to fruits that are surrounded by hard shells, like figs, and fruits surrounded by spines. They use their brains to determine how they can use their teeth and hands using a precision grip similar to a grip found in old world monkeys, but not other neotropical primates.
Their eyes are very specialized and important in finding ripe fruit to eat. Within Capuchins there are several different types of color vision. They also have a greater sensitivity to see bright objects once their eyes have adjusted to the dark.
The Capuchin is considered a quadruped, and walks on all four limbs, using a prehensile tail as another hand. Some new world monkeys have a patch of skin at the end of the tail that has a more specialized skill, but the capuchins have hair to the tip of their tail. They use it for balance while walking on branches reaching for vines or other branches so they don’t fall.
The Capuchins also do a lot of grooming and enjoy grooming with citrus oils and other plant matter in the wild. Some of the objects they have been seen grooming with act as insect repellents, but they may just want to smell good. All four Capuchins here like to rub the oil from limes or etrog all over themselves, and Viola will continue to rub her body with her tail.
All of these specialized morphological features help the Capuchins survive in the wild. They can access food that other monkeys pass by. The use of an abundance of foods allows for a wider range and access of food in times of food scarcity. These specific features make them a very successful monkey.
-Fragaszy, D.M., Visalberghi, E., Fedigan, L.M. (2004) The Complete Capuchin: The Biology of the Genus Cebus. UK. Cambridge University Press
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