Howler Monkeys, Home Range, and Human Encroachment By David Love, Amy Milin, Lauren Peppers, and Sean Perkins

Question: Does human encroachment, such as crop fields, affect the size and shape of the home range of a troop of Alouatta palliata on Isle de Ometepe during the wet season? Hypothesis: Clearing for crop fields on Isle de Ometepe cuts off potential travel routes for Alouatta palliata. This will result in an irregularly shaped home range that forces the monkeys to travel around fields to get to certain resources. Because howler monkeys have a relatively low BMR, the extra energy required to travel a longer distance to reach certain resources will force the monkeys to stick to a smaller home range than they would normally use, one that is more manageable in terms of energy expulsion.

On the southeast side of the volcano Maderas on Isle de Ometepe Group consists of 3 males (possibly 4), 5 females, 4 juveniles, and 1 infant.

Group identified by a specific male, “Frederick”, who had a large head and a black spot in between his testicles on his scrotum. Also, one sub adult male was much smaller than the other two males along with one female who had particularly light markings on her mantle.

The group was tracked each day over a 3 ½ week period and each tree they were seen in was flagged. They were tracked for a total of 144 hours. Tape measures were used to measure distances of fields and between fields. Block count and least polygon methods were used to determine size of the range from GPS coordinates.

The map shows the howler troop’s range in between fields, disturbed areas, and other howler groups The monkeys were tracked around three different sides of one field Other howler groups were found in nearby areas and long calls between the troops were observed The home range based on our study was 8.75 hectares No traditional statistical analysis was used, so our conclusions were based on inferences made from the data. A longer term project is needed for more definitive conclusions