We investigated the role of species-and community-wide seed production by a community of oaks (Quercus spp.) in influencing tree attendance and aggression among California scrub-jays (Aphelocoma californica), corvids that are seed dispersal mutualists, and acorn woodpeckers (Melanerpes formicivorus), near-exclusive seed predators. We tested the hypothesis that scrub-jays reduce their attendance in response to seed crop size on Quercus lobata, the species preferentially attended by acorn woodpeckers, and therefore reduce the risk of potential injury from aggression when community-level seed production enables them to forage on other trees (the Baggression-avoidance hypothesis). Results indicated that scrub-jay attendance correlated positively with Q. lobata crops during the year when community-level seed production was low, resulting in high levels of aggression. In contrast, during the 2 years when acorns of other species were abundant in the landscape, scrub-jays reduced attendance at Q. lobata and experienced less aggression. Similarly, we found that the scrub-jays experienced equally low rates of aggression at Q. douglasii trees that were attended by fewer acorn woodpeckers. These results support the aggression-avoidance hypothesis and illustrate how resource and social dynamics may interact to determine the attendance of mutualistic seed dispersers at oak species competing for seed dispersal. Furthermore, they show that intra-and interspecific social interactions at the seed source, as well as at caching locations, affect the scatter-hoarding behavior of wild corvids.
