eWestern Birds

Colonization of the Brown Booby at the Coronado Islands, Baja California, Mexico

Darrell L. Whitworth, Harry R. Carter, Josh S. Koepke, and Richard J. Young

ABSTRACT: In 2005, we documented the colonization of Middle Rock, Coronado Islands, Baja California, Mexico by the Brown Booby (Sula leucogaster brewsteri)—a significant northern extension of the species’ breeding range possibly related to warming trends in the northeastern Pacific Ocean. Confirmed nesting in 2005 was preceded by an increase in sightings at sea along the northwest coast of Baja California and California in the 1990s and early 2000s and attendance at Middle Rock since at least 2002. In 2002, we observed Brown Boobies on Middle Rock in incubation postures attending two Western Gull (Larus occidentalis) nests containing one gull egg each. One of these gull nests was attended for at least 33 days at the exact site where a single Brown Booby nest was confirmed each year from 2005 to 2007. In 2005 the nest successfully fledged a chick but in 2006 failed for unknown reasons. In 2007, two nests fledged single chicks. Excluding juveniles, documented attendance of at least 6 boobies in 2002, 7 in 2006, 12 in 2006, and 35 in 2007 suggests that the colony will grow further.

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