Interactions between Steller's jays and yellow pine chipmunks over scatter-hoarded sugar pine seeds

Abstract

1. Sugar pine (Pinus lambertiana Douglas) seeds are dispersed by wind, but yellow pine chipmunks (Tamias amoenus Allen) and Steller's jays (Cyanocitta stelleri Gmelin) gather the seeds and scatter-hoard them. Chipmunks and jays store seeds in a similar manner, and during cache recovery they appear to compete for stored seeds. 2. A series of aviary studies and radioactive seed studies in the field were used to examine how chipmunks and jays interact over stored seeds. 3. Aviary studies revealed that chipmunks use spatial memory and olfaction to find seeds, including those stored by conspecifics and jays, whereas jays use spatial memory and observational learning, so they usually find only the seeds that they have stored. Use of olfaction makes chipmunks much better pilferers than jays. 4. In the field, both chipmunks and jays have a recovery advantage (they retrieve their own caches 3.6 faster than do pilferers), and chipmunk caches disappear 3.4 faster than jay caches. 5. Steller's jays appear to avoid chipmunk pilferage by caching seeds in closed-canopy pine forests with little shrub understorey where chipmunks seldom forage, whereas chipmunks cache under shrubs in forest openings. The risk of pilferage by chipmunks appears to force jays to cache in forests. 6. Competition between chipmunks and jays for stored seeds might have indirect effects on sugar pine seedling establishment because seedlings survive better when under shrubs. © 2005 British Ecological Society.