Resource tracking by eastern chipmunks: the sampling of renewing patches

Abstract

When food patches vary in quality over time, sampling by repeated visits can allow animals to track this variation and improve their foraging success. Sampling, however, requires spending time visiting patches that are currently poor. The optimal investment in sampling should depend on characteristics of the patch, the animal, and the environment, but there are few empirical studies of these relationships in nature. Here, we describe discovery, exploitation, and sampling of randomly varying artificial food patches by free-ranging eastern chipmunks ( Tamias striatus (L., 1758)). Chipmunks effectively tracked variation over a broad time scale, discovering patches within a few days, sampling and exploiting over several weeks, and decreasing sampling when renewals ceased. Sampling allowed the chipmunks to track variation on an hourly scale through rapid discovery of renewals. Sampling rates were high (median = 0.3 visits·individual–1·h–1; range = 0–4.2). Sampling was not affected by the frequency or magnitude of patch renewal but was lower for chipmunks whose burrows were farther from the patch. Sampling is an important part of chipmunk foraging strategy, but the difficulty of estimating patch quality and renewal rate and the effects of competition may prevent a close matching between sampling rate and patch characteristics under natural conditions.