eWestern Birds
The Quarterly Journal of Western Field Ornithologists
Status of Ospreys Nesting on San Francisco Bay
Anthony J. Brake, Harvey A. Wilson, Robin Leong, and Allen M. Fish
ABSTRACT: Historical records from the early 1900s, as well as surveys updated in the late 1980s and more recent information from local breeding bird atlases, indicate that Ospreys rarely nested on San Francisco Bay prior to 2005. In 2013, we surveyed nesting Ospreys baywide and located 26 nesting pairs, 17 of which were successful and fledged 44 young. We also report on findings from previous annual nest surveys of a portion of San Francisco Bay beginning in 1999. These results demonstrate a greater breeding abundance than has previously been recognized. The density of Osprey nests is highest near the north end of San Francisco Bay, but nesting also appears to be expanding southward. Nearly all of the nests observed were built on artificial structures, some of which were inappropriate and required nests to be removed. Over half of unsuccessful pairs experienced significant human disturbance. We recommend that conservation efforts focus on reducing this ratio, and to help do so, we urge erecting nest platforms as part of efforts to deter nesting when it conflicts with human activity.