Ecological Studies of Seabirds on Alcatraz Island, 2010

Acosta, Sara; Jahncke, Jaime; 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, 2010. Populations of breeding Brandt’s Cormorants made only a small improvement from the complete breeding failure it suffered in 2009. The Pelagic Cormorants on Alcatraz made no improvement at all and in 2010 had its second complete breed failure in a row. Brandt’s Cormorants did poorly throughout central California where many colonies experienced low breeding numbersand poor reproductive success. The Western Gull population decreased while the California Gull population nearly tripled. Both gull species however, had poor breeding success. Pigeon Guillemot populations increased to the highest yet recorded and confirmed sites were above the long-term mean. Western Gull breeding numbers decreased for the second year in a row to 722 nesting pairs in 2010 (nests taken under a depredation permit from USFWS # MB057058-0 are not included in the total count) from 888 pairs in 2009. Western Gulls fledged an average of 1.2 chicks/pair in 2009, lower than the long-term mean. We confirmed 28 Pigeon Guillemot sites in 2010, an increase from the 20 confirmed sites in 2009, also above the long-term mean. This includes one new nesting site at the finger pier near the dock. One pair of Black Oystercatchers bred on the Seawall in 2010. Two chicks hatched, but only one chick survived to fledge, making it the eighth oystercatcher chick to fledge Alcatraz since 1997. We first discovered California Gulls breeding on Alcatraz in 2004. Since then, the population increased, fluctuating between 12-23 nests. In 2010, the nesting population nearly tripled to 66 nesting pairs. They fledged an average of 0.9 chicks fledged/pair in 2010, the lowest yet recorded since monitoring began. Due to the low attendance of breeding cormorants in 2010, the ability to view only one major sub-colony, and no weekend day monitoring efforts when activity around the island is heaviest, few disturbances of cormorants were documented during approximately 177 hours of observation throughout the breeding season. Of four documented disturbances, only one caused birds to flush, while three were minor disturbances from a jet, a hawk, and an unidentified noise. However, one disturbance event (observed by NPS staff) took place due to a ranger led group entering the Laundry Building and allowed access next to windows next to the Laundry Building Sub-Colony, causing several birds to flush and abandon eggs. We continue to encourage plans to post signs visible to both visitors on the island and to passing boaters that explain proximity restrictions with the threat of law enforcement as well as plans to re-install historical buoys around the island. Alcatraz Island offers a unique opportunity for the public to view seabird breeding activities up close, and this should be highlighted as a focal point of visitor education and outreach. Recent improvements of signage and a new “Birds of Water” display will play a role in improved visitor appreciation and understanding of the seabird colonies at Alcatraz. Interpretive tours around the island, increased staff training regarding awareness and sensitivity of bird colonies, as well as increased public outreach to marine and air traffic operators also will help educate visitors as well as protect breeding seabirds.