Northern breeding range expansion of two Sula species at Sutil Island, California, USA.

We report a northern expansion of the breeding ranges of the Brown Booby (Sula leucogaster) and Bluefooted Booby (S. nebouxii) with the first successful breeding of these species at Sutil Island off Santa Barbara Island, California, USA, in 2017 and 2020, respectively. We documented the arrival and breeding of both species through opportunistic monitoring and annual aerial photographic surveys from 2013 to 2022. We first noted Brown Booby attendance on the island in October 2013, and we confirmed breeding 4 years later in October 2017. The number of observed apparent Brown Booby nests (i.e., nest structures attended by adults or where a chick was seen) increased over time from 4 in 2017 to 31 in 2022. The number of birds observed attending the colony also increased overall to a high count of 164 in September 2021. We first observed Blue-footed Boobies in August 2018 and confirmed breeding 2 years later in June 2020 with a Brown and Blue-footed Booby pair that fledged a hybrid chick. We documented 2 nests with chicks in 2021 and observed a nonhybrid Blue-footed Booby in juvenile plumage in July 2022. These are the first confirmed breeding records for Sula species in the continental USA and represent a northward shift of both species' breeding ranges. [ABSTRACT FROM AUTHOR]