Breeding ecology of Pigeon Guillemots (Cepphus columba) on Alcatraz Island, California

This study compared the breeding ecology and diet of Pigeon Guillemots (Cepphus columba) from an urban estuarine colony (Alcatraz Island) and a remote oceanic colony (Southeast Farallon Island) to better understand how spatial differences and current management influence the two colonies. I used video cameras inside nest sites to help monitor the breeding phenology, reproductive success, and prey delivered to chicks on Alcatraz Island in 2015 and 2016. Data collected in this study were compared with data collected by Point Blue Conservation Science on Southeast Farallon Island. Results show similarities in breeding phenology between the two colonies, although the breeding start date was earlier on Alcatraz in 2016 by 12 days. Productivity was higher on Alcatraz in both years with 0.73 and 0.83 fledged chicks/pair while productivity dropped on Southeast Farallon Island from 0.65 fledged chicks/pair in 2015 to 0.30 fledged chicks/pair in 2016. Chick diets on Southeast Farallon Island were dominated by juvenile rockfish in both years, while the main prey items fed to chicks on Alcatraz switched from flatfish in 2015 to sculpin in 2016. Warmer ocean temperatures and a large ENSO event in 2016 may have created poor conditions for seabirds breeding offshore, while seabirds breeding in San Francisco Bay were buffered by these environmental conditions leading to higher reproductive success.