Living in Islands of Forests: Nutritional Ecology of the Howler Monkey (Alouatta palliata) at La Suerte Biological Field Station, North-Eastern Costa Rica

Abstract

The nutritional value of food resources represents one of the crucial facets of habitat quality that has to be investigated to predict primate persistence in forest fragments. Mantled howler monkeys (Alouatta palliata) are known to be tolerant to habitat fragmentation, although the boundaries of this flexibility are not fully understood. In some fragmented areas, howler monkey densities are among the highest ever recorded for a primate species. As a possible consequence of high competition and resource depletion over-crowding effects are predicted to alter the time-budget and decrease the diet quality of howler monkeys living in small fragments. To test this, we studied the feeding ecology of four howler monkey groups at La Suerte Biological Field Station, North-eastern Costa Rica, over three consecutive summers. Two groups occurred in a 20-ha forest fragment at high density, while the other two groups lived in a larger forest patch at lower density. We collected behavioural data via 5-min Focal Instantaneous Sampling to estimate time-budget, habitat use and diet. Food samples were also collected and analysed to evaluate nutritional contents. Ranging areas (Kernel analysis) and daily path-length were estimated via Ranges 8. Overall, our results show that the nutritional quality of the monkeys' diet in the high-density area was not significantly different than that recorded in the less populated fragment. Although the monkeys in the high-density forest did not alter their time-budget substantially they used much smaller home-ranges. Our results do not support the hypothesis that the monkeys living in the high-density forest are experiencing a drop in diet quality. Differences in forest structure between the two fragments may explain the similarities between the nutritional ecology of the groups.