Publication Date


Document Type


First Advisor

Porter, Leila M.

Degree Name

M.A. (Master of Arts)

Legacy Department

Department of Anthropology


Mantled howler monkey--Food--Costa Rica--Osa Peninsula; Mantled howler monkey--Behavior--Costa Rica--Osa Peninsula; Competition (Biology)--Costa Rica--Osa Peninsula; Folivores--Costa Rica--Osa Peninsula


Two general assumptions have often been made about folivorous primates: first, that feeding competition is low or absent because leaves are a superabundant and evenly dispersed resource, and as a result, that feeding competition does not constrain the size of folivorous groups. However, many folivorous primates maintain smaller group sizes. In this study, I aimed to examine this 'folivore paradox' by testing the hypothesis that mantled howler monkeys (Alouatta palliata) deplete localized patches of young leaves and therefore experience feeding competition. One group of 8 adult individuals was studied July and August 2015 at Piro Research Station in the Osa Peninsula, Costa Rica. Patch occupancy time, intake, and movement were recorded in one minute intervals from the time individuals entered a feeding patch until they left the patch. Patch size and richness was assessed for each patch. Patch depletion was defined as a combination of decreased food intake and increased within-patch movement. Patch depletion occurred in all food types consumed by this group; ripe fruit, young leaves, and mature leaves: in total 36 of 131 patches were depleted. Patch duration was significantly correlated with feeding group size and patch size (DBH). Daily path length was significantly correlated with the number of patches depleted in a day. The occurrence of patch depletion and the fission of howler groups into subgroups while feeding suggest that howler monkey group size is constrained by scramble competition. Feeding competition also appears to constrain group size, further indicating that there appears to be no paradox for this mostly folivorous primate. These results are imperative to furthering knowledge of folivore feeding competition which can improve conservation efforts aimed at helping to protect folivorous species.


Advisors: Leila M. Porter.||Committee members: Mitch Irwin; Thomas Pingel.||Includes bibliographical references.||Includes illustrations and maps.


49 pages




Northern Illinois University

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