Estimated population size of the Island Scrub-Jay Aphelocoma insularis

As an island endemic, the Island Scrub-Jay's Aphelocoma insularis populatio n status and conservation are of concern. In addition, because the Island S crub-Jay is easily observed, it is an ideal candidate for monitoring the ef fects of management efforts on Santa Cruz Island, California. We used estim ates of territory size in several different habitats occupied by the Island Scrub-Jay and the total area of these habitats on the island to develop an empirical estimate of the population size for this species. Our most conse rvative, and we feel most realistic, estimate for the Island Scrub-Jay bree ding population is 7,000 individuals and for the non-breeding population 5, 500 individuals, yielding a total population estimate of 12,500. Even thoug h conservative, this estimate is larger than earlier estimates of 4,000 to 6,000 individuals. Even so, our data suggest no reason exists for immediate concern regarding the population viability of the Island Scrub-Jay and the y provide a baseline for future estimates and comparisons. Most importantly , this population estimate can be used to monitor the influence on the Isla nd Scrub-Jay of future island management efforts, especially regarding exot ic tree species and feral pigs.