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th and that most tests of the hypothesis have involve R beWe 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 add-ing 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. 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Optimal patch exploitation models that predict increased patch exploitation with increased interpatch search times have been a highly successful component of foraging theory (Stephens & Krebs 1986). Eastern chipmunks hav