Ecological Studies and Interpretation of Seabirds on Alcatraz Island, 2009

Acosta, Sara; Jahncke, Jaime; Pitkin, Melissa; Merkle, William; Rachowicz, Lara

Alcatraz Island has become a regionally important site for a number of seabird species in the last couple of decades. Population size, breeding phenology, and productivity of most seabirds including Brandt’s and Pelagic Cormorants, Western and California Gulls, Pigeon Guillemots, and Black Oystercatchers have been monitored since 1995. Disturbance to wildlife is a concern on Alcatraz, given its status as a heavily-visited part of the Golden Gate National Recreation Area (GGNRA) and its location in the center of the San Francisco Bay. During weekly monitoring, we recorded and cataloged disturbances to seabird populations from March - August, 2009. In an attempt to reduce human caused disturbances to seabirds and raise awareness of seabird natural history, PRBO has been conducting education and outreach programs since 2006. In 2009 we delivered public outreach programs to target audiences including on-island staff, island visitors, personal watercraft operators, and school children, and made recommendations for further outreach centered on Alcatraz seabirds. Populations of breeding Brandt’s and Pelagic Cormorants on Alcatraz were completely absent in 2009, the first breeding failures since the populations were established in the early 1990’s. Brandt’s Cormorants did poorly throughout central California where many colonies had little to no breeding attempts and many birds were found dead at colonies and local beaches. Western and California Gull populations also decreased, while the Pigeon Guillemot populations remained steady. Overall productivity for birds that bred in 2009 was lower than the long-term average. Western Gull breeding numbers decreased to 888 nesting pairs in 2009 (nests taken under a depredation permit from USFWS # MB057058-0 are not included in the total count) from 1034 pairs in 2008. Western Gulls fledged an average of 1.3 chicks/pair in 2009, lower than the longterm mean. We confirmed 20 Pigeon Guillemot sites in 2009, a drop from the 32 confirmed sites in 2008, including one nesting new site in the Sallyport building roof. One pair of Black Oystercatchers bred on the Seawall in 2009. One chick survived to fledge, making it the seventh oystercatcher chick to fledge Alcatraz since 1997. We first discovered California Gulls breeding on Alcatraz in 2004. Since then, this small colony behind the rubble piles on the Parade Ground peaked at 23 pairs in 2007, but has since decreased to 14 nests in 2009. They fledged an average of 1.1 chicks fledged/pair in 2009, lower than the mean since the monitoring began.