Success Stories: Human-created Habitats: Seabirds on Alcatraz Island

Sara Acosta

Brandt's Cormorant

Brandt's Cormorant

Prior to human settlement, Alcatraz Island was home to thousands of nesting seabirds, as indicated by the guano-covered sandstone. As early human settlement took place, birds left the island and did not return throughout the military and prison history. Over a century later, Alcatraz became part of the Golden Gate National Recreation Area (GGNRA), a unit of the National Park Service (NPS), and birds slowly began to return to reclaim the island. The Brandt's Cormorant colony on Alcatraz is one of the few known estuarine breeding sites for this species. Pigeon Guillemots are not known to breed elsewhere in San Francisco Bay. The Western Gull and Black-crowned Night Heron colonies are the largest in the Bay. Currently, this diversity of species exists in a delicate balance with the considerable human presence both on and around Alcatraz Island. Over the last 10 years, PRBO Conservation Science and the NPS have been monitoring the return of the nesting birds and especially the growth of the cormorant colony.

Pigeon Guillemots

Pigeon Guillemots

With cooperative efforts between biologists and NPS staff, improved public outreach (signage, bird interpretive displays, tours), and island management (altered tourism, maintenance, and construction activities to protect nesting birds) human-caused disturbance to the cormorants has been reduced and the colony has grown.