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Behavior and ecology of Macaca nigrescens: Behavioral and social responses to the environment and fruit availability

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Author Kohlhaas, Ann K.
Broad Subject Biology
Summary Macaca nigrescens, the Dumoga-Bone macaque, was studied from 1987 to 1990 at Dumoga-Bone National Park, North Sulawesi, Indonesia. Its behavior and grouping patterns were recorded as well as data on weather and fruit abundance. This study was the first year-round study of this species and the first to relate changes in its behavior to proximate variations in the environment and fruit resource. This study also represents a rare attempt to quantify how the relatively mild weather changes in an equatorial rain forest can affect a primate species.

The Dumoga-Bone macaque shows variation in group size ranging from 1 to 62 individuals. Fruit was the primary food type consumed. Other foods included arthropods, leaves, and other plant structural parts. Resting was the most common behavior (47.6%), followed by social activities (22.7%), moving (19.7%), and feeding (10.1%). The most common social activity was grooming (94.4%). Individuals used all the vertical strata in the forest but were primarily arboreal.

High rainfall was correlated with larger group sizes and decreased resting. Larger group size was presumably due to increased huddling promoting group cohesion and to a decreased tendency to disperse. Decreased resting was likely due to compression of the monkeys' effective daytime.

While daily temperature did not have a statistically significant effect on group size, there was some indication of a tendency for larger group sizes when daytime temperatures were higher and smaller group sizes following lower nighttime temperatures. High daytime temperatures were correlated with increased resting and decreased social activity. Low nighttime temperatures were correlated with decreased resting and increased movement and social activity. Low temperatures promoted "friendly" interactions such as playing, copulating, and grooming, while high temperatures promoted agonism. The amount of feeding time was not correlated with any of the environmental factors. Seasonally, the monkeys tended to use higher canopy heights when daytime temperatures were high and nighttime temperatures were low.

Mixed results were obtained comparing activity times with fruit abundance. There was some indication of smaller group sizes after fruits have fallen, and feeding time decreased when more fruits were available in the canopy.

Language English
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