Dr. Kymberley A Snarr, University of Toronto, Centre for Environment
Director of Conservation and Research, COTERC

In the fall of 2007, a large mammal monitoring program was established at the research station. It is critical to understand which large mammals live in and around the station as they are important components in all forest ecosystems, playing vital roles in seed dispersion and seed predation.

The mantled howler (Alouatta palliata) is the most commonly found monkey in the region and is one of the four New World Monkeys which range in Costa Rica. Howlers have the largest body size of all the New World monkeys. The large and stock adult mantled howlers weigh in at approximately 5-7 kg with the males being much larger than the females. These large monkeys are found to have considerable variation in their coat colour, which is described as blackish and brownish with elongated yellowish hairs along the flank. Their group sizes are quite variable and are known to range from groups of 5-28 with single individuals found living solitary during periods of immigration.

Both males and females disperse from their natal groups and join new groups. Previous research on the howlers at Caño Palma was conducted by Dr. Tracey Farmer whose work looked at the group numbers and sizes. The Large Mammal Monitoring Project has found clear evidence of the continued presence of the mantled howler, detected through visualizations and their spectacular vocalizations. Tracks are not likely to be found as this species of monkey is arboreal, meaning they live in the trees and rarely come down to the ground. They drink from small catchments of water in tree holes, and feed on leaves and fruit. Their long call is considered to be the loudest animal call in the world with the sound being produced from resonations within their enlarged hyoid bone.

The presence of the howlers indicates that their ecosystem role is not compromised. Thus, the howlers continue to feed on leaves, young shoots, and fruits – acting as both browse thinners and seed vectors to increase the health of the forest. With the placement of Caño Palma at the lower end of Barro Colorado Wildlife Refuge (BCWR), it acts as an exchange area for wildlife, providing safe habitat and the intimate connections needed for gene flow and mobility between the two large reservoirs of BCWR and the southern Tortuguero National Park.

References:
Crockett C.M. and J.F. Eisenberg 1987. Howlers: Variation in group size and demography. In: Primate Societies, BB Smuts, D.L. Cheney, R.M Seyfarth, R.W. Wrangham, and T.T. Struhsaker (eds), University of Chicago Press, Chicago, pg 56-68


Reid F.A. 1997. A field guide for the Mammals of Central America and southeast Mexico. Oxford University Press, New York


Snarr K.A. 2006 Life in a lowland wet forest fragment on the north coast of Honduras: the mantled howler (Alouatta palliata) of Cuero y Salado Wildlife Refuge. University of Toronto, PhD, supervisor: Dr. F Burton