Date of Thesis



Marginal value theorem (MVT), a key component of optimal foraging theory, aims to model how an individual will most efficiently utilize a resource distributed in patches of varying size and value throughout a habitat. Among the fundamental assumptions of MVT is that foragers will maximize their net energy gain by foraging in a resource patch until reaching the average rate of intake for the habitat. This "give-up time" (GUT) per patch, defined as the time between the final prey capture and departing the patch, should remain constant throughout the habitat as a whole, but vary across habitats of different quality. For example, a rich habitat should have a shorter GUT than that of a poorer habitat because it takes less time to lower the density of each patch to that of the average rate of intake for the habitat. Though tested and supported in avian studies, marginal value theorem has not been thoroughly tested in primates. This study tested whether foraging behavior of captive common squirrel monkeys (Saimiri sciureus) conformed to the assumptions of marginal value theorem. In keeping with the predictions of MVT, I hypothesized that there would be a significant difference in GUTs for rich and poor habitat manipulations and no difference in the GUTs of patch types within each manipulation. Subjects foraged on an experimental tree made out of PVC pipe and consisting of twelve horizontal branches stratified into three layers of four branches. A wooden platform supporting six evenly spaced capped film canisters, each containing a small mealworm, was positioned at the end of each branch with each platform signifying a distinct resource patch. Two individuals were selected for use in data collection based on their willingness and aptitude for navigating between feeding platforms and successfully opening the film canisters containing food rewards. Testing included two experimental manipulations, rich and poor, which varied in the number of canisters on each platform that contained mealworms. The rich habitat contained more mealworms per platform than the poor habitat. Furthermore, both manipulations contained two patch types that also varied in the number of mealworms. Trials consisted of releasing one subject into the enclosure containing the experimental tree and recording arrival at a patch, opening a canister, ingesting a mealworm, and departing a patch until all canisters had been opened. Each subject participated in an equal number of rich and poor manipulation tests. Two-way repeated measures ANOVA comparing GUTs showed that as predicted, the GUT of the poor manipulation was significantly higher than that of the rich and there was no significant difference in GUTs between the two patch types in the rich manipulation. However, the two patch types in the poor manipulation were significantly different, which contradicted the predictions of MVT. Results demonstrated some evidence for optimal foraging in squirrel monkeys, providing a basis for continued research in this area.


Optimal foraging theory, Marginal value theorem, Primates, Squirrel monkeys

Access Type

Honors Thesis

Degree Type

Bachelor of Science


Animal Behavior

First Advisor

Peter Judge