Cocos booby
A booby species split from brown booby in 2024.
Wikipedia / Wikimedia Commons
The Cocos booby (Sula brewsteri), once called Brewster’s booby, belongs to the booby family Sulidae. Until 2024, it was classified as a subspecies of the brown booby, but the American Ornithological Society then recognized it as a separate species based on differences in appearance and behavior. Its range spans the eastern and central Pacific Ocean.
First described in 1888 by Nathaniel Stickney Goss from birds collected on San Pedro Mártir Island in the Gulf of California, it was named *Sula brewsteri* after ornithologist William Brewster. In 1944, Alexander Wetmore reclassified it as a brown booby subspecies. In 2024, a unanimous proposal to the American Ornithological Society restored it to full species status. Because North American bird names no longer honor people, the common name was changed from Brewster’s booby to Cocos booby, after Cocos Island off Costa Rica, where it breeds. Depending on the authority, the species has two or three subspecies: *S. b. brewsteri* (breeds on islands in the Gulf of California and off Baja California), *S. b. etesiaca* (breeds on islands off Central America and Colombia), and *S. b. nesiotes* (breeds on Clipperton Island).
The clearest difference from the brown booby is the male’s whitish face, which varies by subspecies. Females of all subspecies have a white forehead. Males of *S. b. nesiotes* have the most white, with a fully white head and neck. Nominate males have a white face and pale brown neck, while *S. b. etesiaca* males only show white on the forehead. Males also have a gray bill (brown booby males have a yellow one), and females have a pinker bill than female brown boobies.
Like other boobies, the Cocos booby breeds in colonies on islands. When it meets brown boobies, interbreeding is rare. On Wake Island, male and female Cocos boobies consistently paired with each other within large brown booby colonies. Female Cocos boobies among only brown boobies did not pair, and hybridization has only been seen in colonies with male Cocos boobies but no females. Two known hybrid cases occurred: one on Midway Atoll in 2020, and another on Nakanokamishima Island from 2012 to 2014, where a chick was successfully raised.
Cocos boobies live in the East Pacific, breeding in Costa Rica, Nicaragua, Mexico, French Overseas Territories, Colombia, and the United States. They also occur offshore of Guatemala, El Salvador, and
- Scientific name
- Sula brewsteri
- Family
- Sulidae
- First described
- 1888 by Nathaniel Stickney Goss
- Former name
- Brewster's booby
- Native region
- East and central Pacific Ocean
- Subspecies
- 2 or 3 depending on authority
Lore & Background
The Cocos booby was first described by Nathaniel Stickney Goss in 1888 based on birds collected on San Pedro Mártir Island in the Gulf of California. He gave the birds the Latin name Sula brewsteri after his friend and fellow ornithologist William Brewster. In 1944, the ornithologist Alexander Wetmore placed Brewster's booby as a subspecies of brown booby. In 2024 a proposal to the American Ornithological Society to return to treating Brewster's booby as a distinct species was passed unanimously. Due to the changes of all North American bird names including the names of people, the name for the species was also changed from Brewster's booby to Cocos booby, after Cocos Island off Costa Rica, where the species breeds.
Cocos booby currently has either two or three subspecies depending on the taxonomic authority. The subspecies are S. b. brewsteri, S. b. etesiaca, and S. b. nesiotes. The most immediately obvious difference from the related brown booby is the male's whitish face, varying in size by subspecies. Females of all subspecies of Cocos booby also possess a white forehead. Males of the subspecies S. b. nesiotes have the most white, with a fully white head and neck. Males of the nominate subspecies have a white face, and a pale brown neck, while males of the subspecies S. b. etesiaca only have white on their foreheads. Males also have a grey bill, rather than the yellow bill of male brown booby, and females have a pinker bill than female brown booby.
Reader's Guide
The Cocos booby represents a significant taxonomic revision within the Sulidae family, having been recognized as a distinct species in 2024 after decades as a subspecies of the brown booby. Its split was based on morphological and behavioural differences, and the proposal to the American Ornithological Society passed unanimously. The species is notable for its colonial breeding on islands across the east and central Pacific, including recent range expansions into Japan, Hawaii, and California. Observations indicate that interbreeding with brown boobies is rare, occurring only under specific demographic conditions, such as when male Cocos boobies lack females of their own species. The species' name change from Brewster's booby to Cocos booby reflects a broader shift in North American bird naming conventions. Its three subspecies vary in the extent of white on the male's head and neck, providing a clear example of geographic variation within a single species. The Cocos booby's presence on remote islands like Clipperton and Cocos Island underscores its role in Pacific seabird ecology.
Did You Know?
- The Cocos booby was first described in 1888 by Nathaniel Stickney Goss based on birds from San Pedro Mártir Island.
- It was split from the brown booby by the American Ornithological Society in 2024.
- Males of the subspecies S. b. nesiotes have a fully white head and neck.
- At least two instances of hybridization with brown booby are known, one from Midway Atoll in 2020.
Frequently Asked Questions
What is the Cocos booby?
The Cocos booby (Sula brewsteri) is a Pacific seabird in the Sulidae family that ranges across the eastern and central Pacific Ocean. It was formerly lumped in with the brown booby but was elevated to full species status by the American Ornithological Society in 2024.
How is the Cocos booby different from the brown booby?
The two were long treated as one species, but the Cocos booby shows distinct differences in both plumage and behavior that led to its 2024 split. Before that, Alexander Wetmore had reclassified it as a subspecies of the brown booby back in 1944.
Who was the Cocos booby named after?
The species epithet brewsteri honors ornithologist William Brewster. The original 1888 description was written by Nathaniel Stickney Goss, who worked from birds collected on San Pedro Mártir Island in the Gulf of California.
How many subspecies does the Cocos booby have?
Taxonomic authorities disagree slightly on the count, with some recognizing two subspecies and others acknowledging three. The exact number depends on which classification system you follow.
What was the Cocos booby called before its current name?
It was long known as Brewster's booby, a nod to the ornithologist whose name appears in the Latin binomial. The switch to the shorter 'Cocos booby' came alongside its 2024 recognition as a standalone species.
More in Birds of the Pacific Ocean 1-24
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