Ta. Waite et Jd. Reeve, SOURCE-USE DECISIONS BY HOARDING GRAY JAYS - EFFECTS OF LOCAL CACHE DENSITY AND FOOD VALUE, Journal of avian biology, 26(1), 1995, pp. 59-66
By analogy with patch-use decisions made by animals foraging among pat
ches, animals storing food items among scattered sites must make decis
ions such as how long to persist in exploiting a known source before l
eaving to search for alternative sources. If the survival of scattered
caches is density-dependent, then there should be a ''source-departur
e threshold,'' beyond which additional caching would reduce the long-t
erm average rate of storage of recoverable food. The hoarder would pro
fit maximally by leaving the source at that threshold, even though the
source still contains food. We experimentally examined how two factor
s influence various source-use decisions of Gray Jays Perisoreus canad
ensis exploiting locally abundant food sources. First, we examined the
behavior of jays exploiting a food source during an initial ''encount
er'' and during another encounter 3 days later. The jays made fewer ca
ches during subsequent encounters with a source at a given location, a
round which the local density of previously made caches was high. They
also compensated by spacing out their caches more widely and by incre
asing the rate at which they retrieved and redistributed previously ma
de caches. Second, we investigated the effect of the composition of a
food source (i.e., the value of its food items) on the jays' source-us
e decisions. The jays cached substantially more food items (raisins) f
rom a large-item (($) over bar X=491) than from a small-item (328) sou
rce when sources of each type were made available on different days. T
he cumulative number of caches made by individual jays (over 10 h) was
more nearly asymptotic in the smaller-item treatment. We propose that
the jays' tendency to recache previously made caches accounts for the
ir failure to cease hoarding from our experimental sources. This two-s
tage process of food storage (i.e., initial placement and subsequent r
ecaching) may yield long-term average rates of storage throughout the
territory exceeding those predicted by simple rate-maximization, patch
-use models.