The effect of handling time on the decision to cache by grey squirrels

Animals that store food must decide which items to eat immediately and which to store for future consumption. Clearly, a starving animal should eat and a satiated animal should store, but other factors must influence this decision in partially satiated foragers. Characteristics of the food could affect the decision; eastern woodrats, Neotoma floridana, eat highly perishable food and store food that is less perishable (Reichman 1988). If caching a food item takes less time than eating it, however, then foragers under time constraints might be affected by an item's handling time. Such time constraints should affect the caching decision in the grey squirrel, Sciurus carolinensis. Grey squirrels eat and store the large seeds of hickory, Carya spp., and oak, Quercus spp., trees during a short autumn harvest (Thompson & Thompson 1980), competing with conspecifics at communal food trees (Jacobs 1987). I hypothesized that a squirrel could increase its foraging efficiency by always choosing the behavioural option, eating or caching, that was least time consuming. If one food item took longer to eat than another, and if a squirrel could cache an item in less time than it took to eat it, then a squirrel should preferentially cache those items that took longer to eat. I tested this hypothesis with five hand-raised adult male grey squirrels. The squirrels were kept in individual outdoor cages, measuring 1 • 1 • 1.5 m, and maintained on a diet of laboratory rodent chow, unshelled peanuts, hazelnuts and black walnuts, and water ad libitum. All squirrels had experience eating, caching and retrieving the foods (hazelnuts, laboratory rodent chow) used in this experiment. Squirrels were deprived of food for 24 h before testing. They were then given a series of 20 food items, in their cage, one at a time, as illustrated in Fig. la. Ten items each of two food types, which differed in consumption time, were given alternately to the squirrel, beginning with the item