Birdsong field guide
Cocos Booby
Sula brewsteri
The Cocos Booby, often recognized as the Brewster's subspecies of the Brown Booby, is a striking tropical seabird known for its dramatic sexual dimorphism. It is a master of the eastern Pacific, easily identified by the male's unique frosted plumage.
What it sounds like
Females produce a deep, harsh, repetitive quacking or grunting; males vocalize with thin, high-pitched, wheezy whistles.
Reference call, compare with what you heard
No reference call found yet · Xeno-canto
Field notes
- Adult males feature a distinctive white or pale gray 'frosted' head that fades into a dark chocolate-brown neck and body.
- The species lacks external nostrils, breathing instead through the corners of the mouth to prevent water ingress during high-speed dives.
- They are opportunistic foragers that frequently follow schools of predatory fish like tuna to catch flying fish and squid driven to the surface.
- Nesting occurs on the ground in scrapes, where females typically lay two eggs but rarely fledge more than one due to obligate siblicide.
- Their feet are totipalmate, meaning all four toes are connected by webbing, which provides powerful propulsion both on and under the water.
Habitat
Remote volcanic islands, rocky offshore stacks, and surrounding pelagic marine environments.
Range
Eastern Tropical Pacific, including the Gulf of California, the Revillagigedo Islands, and south to Cocos Island.
Similar & commonly confused birds
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