High Relative Humidity Increases Pilfering Success of Yellow Pine Chipmunks

Abstract

Scatter-hoarding animals store food items to be used later when food is scarce. However, other individuals can pilfer food stores because caches are not usually defended. We tested how associative learning contributes to foraging success of pilferers searching for scatter-hoarded food. We conducted a field-based, seed-removal experiment to test 2 hypotheses. First, yellow pine chipmunks (Tamias amoenus) will learn to associate buried food with recurring objects faster than they will learn to associate food with singular (distinctive) objects. Second, they will learn to associate buried food with man-made objects faster than they will learn to associate food with natural objects. Rodents clearly learned to associate objects with buried food regardless of distinctiveness or origin. The observed pattern of seed removal suggested that high relative humidity (RH) events (storm systems) increased seed odor, facilitating olfaction by rodents, and increasing the rate of seed removal. We tested this hypothesis in a laboratory experiment using 8 wild-caught yellow pine chipmunks and 5 levels of RH (17%, ,27%, ,50%, ,75% ,o r,95%). Foraging success at 17–75% RH was not different from random, but at 95% RH seed recovery was significantly higher than random. High RH facilitates discovery of buried seeds, and with higher foraging success, associative learning of cache markers may be easier. Thus, cache pilfering may be facilitated by high humidity.