Social Hoarding and a Load Size-Distance Relationship in Gray Jays

Abstract

A model that assumes scatterhoarders maximize the rate at which they store food that survives densitydependent theft by competitors has been developed elsewhere (Waite 1991a; Waite and Reeve 1992a, 1992b). The model addresses the questions of how such hoarders should distribute caches of food items collected from an ephemeral, locally abundant source, and how long they should persist in caching from such a source before moving on in search of alternative sources. The results of several field experiments using Gray Jays (Perisoreus canadensis) were qualitatively consistent with the model in most contexts (references above). However, because the model implicitly assumes that a hoarder's behavior is not influenced by that of other individuals, methodological measures were taken in those experiments to eliminate any confounding effects of social context on the jays' caching behavior. Here, I describe a simple field experiment designed to investigate whether the distance to which Gray Jays transport food items for storage is affected by load (food-item) size and social context (solitary or in the company of one or more conspecifics). I present evidence that apparent attempts by the jays to cache secretively were influenced by the size (value) of the food item, the immediate risk of losing a cache to a conspecific soon after the cache had been put in place, and the interaction of these two factors (food-item size and social context). Any tendency to cache secretively may reduce the probability of cache theft, which may be accomplished also by adequately spacing caches (Waite 1988, Waite and Reeve 1992a), appropriately timing the decision to move on to alternative sources while a known source still contains food (Waite and Reeve 1992b), placing caches in inconspicuous sites (Petit et al. 1989, Waite 1991 la), and concealing caches (Petit et al. 1989, Waite 1991a). The Gray Jay is a permanent resident of high-latitude boreal forests in North America. These birds store hundreds of food items per day during summer (Waite 1991a), and apparently rely heavily on that food during the winter (Waite 1990), when they have as little as 4 hr of foraging time available each day during which to accumulate energy reserves for the upcoming night of hypothermic fasting (Waite 199 ib, in press). Food items are cached as saliva-coated boli (Dow 1965), each of which is placed in a separate arboreal site, such as under a flake of bark, in a clump of lichen, or in a conifer needle-cluster.