Pygmy Marmoset, which is also called Cebuella pygmaea,¬¬ is the smallest primate in the world. It is an arboreal species native to the Amazonian Basin in Columbia, Ecuador, Peru, northern Bolivia, and Brazil. The small stature of the species, which weights only about 120 -140g, and has a 14-16cm length. This is a highly social and territorial animal, which lives in troops of two to six members, and has unique evolutionary adaptations that provide the species with the ability to operate as a cohesive unit amid the dense, humid spaces of the Amazonian rainforest. These factors combine to create a patchy distribution in their native habitat.
Society of Pygmy Marmosets
Pygmy marmosets are cooperative breeders, as are all other species of callitrichid primates, the marmosets and tamarins. Most typically, social groups are composed of a single male-female breeding pair and non-reproductive helpers that assist with a number of duties, including caring for the breeding pair’s offspring and engaging in anti-predator vigilance.
Food of Pygmy Marmosets
Pygmy marmosets rely on exudates as a primary food resource. Exudate is an uncommon food source for primates, and its characteristics as a resource are quite different from other, more typical primate food resources, such as fruits, leaves and herbaceous plants. Each social group of pygmy marmosets typically utilizes only one or two exudate source trees within its home range at any given time, but may make many feeding sites (gouge holes) on each tree. Thus, although the number of sources is limited, the availability of the exudate resource is relatively stable, and feeding sites on the resource are abundant. In addition to utilizing exudates, pygmy marmosets also spend about 33% of their feeding time foraging for insect prey. Insects come in discrete ‘packets’, and may be a more monopolizable resource than is exudate.
Communication of Pygmy Marmoset
The vocalizations of the pygmy marmoset, as well as of other Callitrichids, contain high frequency components that are severely attenuated during transmission in the forests and that may not be considered as optimal for auditory communication. It is suggested that a possible advantage of the marmoset’s high-frequency calls was to avoid masking by ambient noise by using a region with low amplitudes in the noise spectra, above the major frequencies of ambient noise in the environment.
Captive and wild pygmy marmosets use Trills and J calls that are variants of a sinusoidally frequency modulated tone for short-range communication. These call types are used to maintain contact within group members, providing information about the location of the animals. It is suggested that the greater frequency modulation of the J calls compared to the Trills and the fact that it is a repeated, interrupted call providing several time of arrival cues may improve the receiver’s ability to locate I calls compared with Trills. It is found that a differential use of these call variants was correlated with differences in the spatial distribution of group members; marmosets used Trills when at close distances to one another (up to 9 m apart), and J calls when far apart from each other (more than 20m apart).
A different call type, the Long call, may be used for communication over even larger distances. The fact that most of the sound energy in the Long call is concentrated in the lower frequency components (increasing the intensity of the sound) may increase the distance over which this call type would be audible. Finally, the effects of reverberation that are more severe for signals with fast repetition rates could be greater in more repetitive calls such as the Trills and J calls than for the Long calls.