Late Spring Storm Caused 30% Loss to Alcatraz Brandt’s Cormorant Colony

537 Brandt’s cormorant nests were flooded during a large storm this past May as the adults were incubating eggs or caring for newly hatched chicks.

NPS

October 2019 - This year, a large multi-day rainstorm flooded 537 Brandt’s cormorant nests on Alcatraz Island. The May storm occurred during the peak nesting season when cormorants were incubating eggs or caring for newly hatched chicks. The number of nests on Alcatraz was still increasing (2,067 nests before the storm) when the storm occurred, resulting in a 30% loss to the colony. Although cormorants abandoned one area flooded by the storm, it’s likely many of these birds re-nested, as the total nest count on Alcatraz climbed back up to 1,846 following the storm. The total number of nests post-storm was a 14% decrease from 2018, which had the highest number of Brandt’s cormorants ever recorded on Alcatraz (2,120 nests). Brandt’s cormorant productivity (chicks fledged per pair) was low (1.1 ± 1.1 chicks/pair) this year compared to the long term mean (1.9 ± 0.6 chicks/pair).

The National Park Service monitors breeding Brandt’s cormorants on Alcatraz through a partnership with the Farallon Institute. Contact Tori Seher to learn more.

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