eWestern Birds
The Quarterly Journal of Western Field Ornithologists
Acorn Dispersal by California Scrub-Jays in Urban Sacramento, California
Daniel A. Airola
ABSTRACT: California Scrub-Jays (Aphelocoma californica) harvest and cache acorns as a fall and winter food resource. In 2017 and 2018, I studied acorn caching by urban scrub-jays in Sacramento, California, to characterize oak and acorn resources, distances jays transport acorns, caching’s effects on the jay’s territoriality, numbers of jays using acorn sources, and numbers of acorns distributed by jays. Within four study areas, oak canopy cover was <1%, within four study areas and only 19% of 126 oak trees, 92% of which were coast live oaks (Quercus agrifolia), produced acorns. Jays transported acorns for ≥117 days. Complete (28%) and partially recorded (72%) flights from acorn sources to caching sites averaged 160 m and ranged up to 670 m. Acorn-transporting jays passed at tree-top level above other jays’ territories without eliciting defense. At least 20 scrub-jays used one acorn source in one 17.5-ha area, and ≥13 jays used another 4.7-ha area. Jays cached an estimated 6800 and 11,000 acorns at two study sites (mean 340 and 840 acorns per jay, respectively), a rate much lower than reported in California oak woodlands, where harvest and caching are confined within territories. The lower urban caching rate may result from a scarcity of acorns, the time required for transporting longer distances, and the availability of alternative urban foods. Oaks originating from acorns planted by jays benefit diverse wildlife and augment the urban forest.