Photo by © olivewarbler
Near Gorgona Island, Colombia northern Pacific, 11 March 2008
Alternative name: Brewster’s Booby
- Sula brewsteri
Identification
Females tend to have pink bill versus yellowish in Brown Booby.
Variation
Male Cocos Booby has a head varying from being entirely whitish to having white restricted to forehead.
Similar Species
Male Cocos Booby has head more whitish, bill more grayish-blue, and gular pouch more greenish-blue, when compared to Brown Booby. Female Cocos Booby has a whitish forehead where Brown Booby is brown. Underwing of both sexes also differ, with lesser wing coverts showing a brown bar in Cocos B. which is absent in Brown B.
Distribution
In areas on and around the Cocos tectonic plate which gave this species it's name. Breeds on islands from the Gulf of California to islands off Colombia (including on the Cocos Island west of Costa Rica). A recent range expansion resulted in occurrence further west, e.g., in Hawaii, the Northern Mariana Islands, and the northern Line Islands.
Taxonomy
Cocos Booby was formerly included in Brown Booby. The split of the two was at least in part based on the observation of assortative mating where they coexist in the same colonies.
Subspecies
Clements recognizes these subspecies[1]:
- S. b. brewsteri: islands in Gulf of California and off western Mexico
- S. b. etesiaca: Pacific islands off Central America and Colombia
Habitat
Islands offering safe breeding for that activity, and on sea for everything else. This species is more common in shallower sea, but can also be found over deeper water.
Behaviour
Adults seems to have site fidelity for their breeding colony, but outside of breeding very little is known.
Breeding
Nests are placed on bare ground in rocky areas including on cliffs. Litter size is 1-2 eggs. Timing is variable in different colonies, including being year round in some.
Vocalisation
References
- Clements, J. F., P. C. Rasmussen, T. S. Schulenberg, M. J. Iliff, T. A. Fredericks, J. A. Gerbracht, D. Lepage, A. Spencer, S. M. Billerman, B. L. Sullivan, M. Smith, and C. L. Wood. 2024. The eBird/Clements checklist of Birds of the World: v2024. Downloaded from https://www.birds.cornell.edu/clementschecklist/download/
- Gill, F, D Donsker, and P Rasmussen (Eds). 2024. IOC World Bird List (v 14.2). Doi 10.14344/IOC.ML.14.2. http://www.worldbirdnames.org/
- Mlodinow, S. G., E. A. Schreiber, and R. L. Norton (2024). Cocos Booby (Sula brewsteri), version 1.0. In Birds of the World (B. K. Keeney and S. M. Billerman, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.cocboo1.01
Recommended Citation
- BirdForum Opus contributors. (2025) Cocos Booby. In: BirdForum, the forum for wild birds and birding. Retrieved 5 February 2025 from https://www.birdforum.net/opus/Cocos_Booby
External Links
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