What seeds tell us about birds: a multi-year analysis of acorn woodpecker foraging movements

Background: Foraging movements of animals shape their efficiency in finding food and their exposure to the environment while doing so. Our goal was to test the optimal foraging theory prediction that territorial acorn woodpeckers (Melanerpes formicivorus) should forage closer to their 'central place' in years of high resource availability and further afield when resources are less available. We used genetic data on acorns stored in caching sites (granaries) and adult trees for two oak species (Quercus lobata and Quercus agrifolia) to track acorn movements across oak savanna habitat in central California. We also compared the patterns of trees these territorial bird groups foraged upon, examining the effective numbers of source trees represented within single granaries (alpha), the effective number of granaries (beta), the diversity across all granaries (gamma), and the overlap (omega) in source trees among different granaries, both within and across years. Results: In line with optimal ...