Testing central place foraging in eastern chipmunks, Tamias striatus, by altering loading functions

Eastern chipmunks are thought to be rate-maximizing central place (CP) foragers because several experimental tests have provided qualitative support for the prediction that their load sizes increase with distance between patch and burrow. Confidence in this conclusion is tainted by the fact that chipmunks always collect loads that are considerably smaller than those expected of rate-maximizing CP foragers and that most tests of the hypothesis have involved effects of distance and travel times on load sizes. We experimentally manipulated the loading functions of 12 chipmunks by providing them with either natural sunflower seeds (Helianthus sp.) or sunflower seeds onto which we fastened an appendage that had to be removed before loading. Adding the appendage to the seeds altered the loading function by adding decreasing amounts of handling time as each successive seed was loaded. Both load sizes and patch times were larger for seeds with an appendage, and the effect on load size was greater at 5 m than at 20 m from the burrow, as predicted for rate-maximizing foragers. These results provide novel qualitative support that chipmunks behave as rate-maximizing CP foragers.