Evidence against maximization of gross rate of seed delivery to the burrow in food-hoarding eastern chipmunks, Tamias striatus

The central place foraging model predicts the optimal load sizes of prey carried back to a central place. When the rate of prey loading at the patch declines with time spent in the patch, the optimal, rate-maximizing load sizes increase with round-trip travel times between patch and central place. Numerous tests of this rate-maximizing currency have been carried out with eastern chipmunks carrying loads of seeds to their burrow. All tests have provided consistent qualitative support for the model (load sizes increase with distance) as well as consistent quantitative rejection of the model (loads carried are always considerably smaller than optimal). Confidence in the repeated rejections of the currency is weak because the predicted optimal load sizes stem from extrapolations of the loading function beyond the data used to estimate it. In this study, we provided subjects in the field with a food patch that provided the same increasing interval schedule of prey arrival at 2 m and 15 m from their burrow. Results confirm the quantitative failure of the rate-maximizing currency for the central place foraging model. We propose that the consistent failures of rate maximization with chipmunks are probably due to the higher predation danger when collecting seed from a patch compared to travelling.