Surveillance for West Nile virus and vaccination of free-ranging island scrub-jays (Aphelocoma insularis) on Santa Cruz Island, California.

Transmission of West Nile virus (WNV) on mainland California poses an ongoing threat to the island scrub-jay (ISSJ, Aphelocoma insularis), a species that occurs only on Santa Cruz Island, California, and whose total population numbers <5000. Our report describes the surveillance and management efforts conducted since 2006 that are designed to understand and mitigate for the consequences of WNV introduction into the ISSJ population. We suspect that WNV would most likely be introduced to the island via the movement of infected birds from the mainland. However, antibody testing of >750 migrating and resident birds on the island from 2006 to 2009 indicated that WNV had not become established by the end of 2009. Several species of competent mosquito vectors were collected at very low abundance on the island, including the important mainland vectors Culex tarsalis and Culex quinquefasciatus. However, the island was generally cooler than areas of mainland California that experienced intense WNV transmission, and these lower temperatures may have reduced the likelihood of WNV becoming established because they do not support efficient virus replication in mosquitoes. A vaccination program was initiated in 2008 to create a rescue population of ISSJ that would be more likely to survive a catastrophic outbreak. To further that goal, we recommend managers vaccinate >100 ISSJ each year as part of ongoing research and monitoring efforts.