The dark booby with the white belly that dives around the Arch is not quite the brown booby of the Caribbean. In 2024 ornithologists split the eastern Pacific birds into their own species, the Cocos booby, and in Mexican waters the males are easy to pick out by their pale, whitish faces.
A slim seabird with long, pointed wings, a wedge-shaped tail and a long, dagger-like bill. The head, neck, chest and upperparts are dark chocolate brown, cut off in a sharp line from the white belly; the underwing is white in the middle with a brown border. Males in Mexico have a whitish face and throat that fade into a pale brown neck, with blue skin around the eye and a grayish bill. Females have a brown head that is paler than a female brown booby’s, with a whitish forehead, greenish-yellow facial skin and a pinkish bill. Feet are yellowish green. Young birds are brown all over, with brown-mottled underparts.
Cocos boobies breed on islands of the eastern Pacific, from the Gulf of California and western Mexico through Central America to Colombia, including Clipperton and the Revillagigedo Islands. The species was described from Isla San Pedro Mártir in the Gulf of California, still its largest colony; other Gulf colonies include San Jorge and San Ildefonso. In most of the Gulf they breed from about December to May, during the upwelling season, and in El Niño years most birds skip nesting. In recent decades they have spread north to the Coronado Islands off Tijuana and the California Channel Islands, and west to Hawaii and other central Pacific islands.
In the Gulf they live mainly on small schooling fish in the cool season; at San Jorge, where the sea is shallow, they also take bottom fish when sardines and anchovies are scarce. They plunge almost vertically from about 1 to 15 m above the water and can chase prey underwater for up to 40 seconds, or skim fish from the surface. Females lay one or two eggs, both parents incubate for about 42 days, and chicks fledge at about 90 days.
The usual rule would have revived the old name Brewster’s booby, but the AOS no longer uses names that honor people. The choice fell on Cocos booby, after the Cocos Plate and Cocos Island off Costa Rica, an important nesting site, and to match the Nazca booby.
Source ↗Brown boobies form four genetic groups, and the eastern Pacific group is the most distinct: it split off roughly one million years ago.
Source ↗Where Cocos boobies now nest among brown boobies in the central Pacific, they pair mostly with each other and interbreeding is rare, one of the main reasons for the split.
Source ↗The species was first described in 1888 from Isla San Pedro Mártir, in the middle of the Gulf of California. In the 1990s that island held about 74,000 nests, the largest colony of all.
Source ↗In most of the Gulf of California they breed from about December to May, when upwelling makes the sea most productive.
Source ↗Cocos boobies have colonized the Coronado Islands off Tijuana and begun nesting on Sutil Rock in California’s Channel Islands.
Source ↗This is the booby you’ll see most often around Cabo: CONANP lists it as a resident of the Cabo San Lucas protected area, and it rests on the rocks around the Arch and dives over bait schools in the bay. Look at the head: a bird with a whitish face is a male, and a brown-headed bird with a pale forehead is a female.
Boobies dive on the same bait you’re fishing, so they sometimes grab a lure or a bait. If one is hooked, don’t lift it by the line. Reel it in slowly and gently, using a dip net if you have one, control the bill first, since seabirds peck, and cover its head and eyes with a cloth without blocking its breathing. Cut off the barb and back the hook out; if the hook is swallowed, cut the line as close to it as you can. A seriously injured bird should be reported to PROFEPA.
| Mexico (NOM-059) | Not listed as a species at risk, neither as Cocos booby nor as brown booby (2019 update) |
|---|---|
| Cabo San Lucas protected area | Listed as a resident bird of the Cabo San Lucas Flora and Fauna Protection Area (CONANP, 2023) |
| IUCN Red List | Not assessed separately; the brown booby in its old, broader sense is Least Concern (2018) |
| Taxonomy | Treated as a species by the American Ornithological Society (2024), the IOC World Bird List (2024) and the Clements/eBird checklist (2024) |
The brown booby (Sula leucogaster) of the Atlantic, Caribbean and central Pacific looks almost the same, but adult males have an all-dark brown head. The blue-footed booby has a pale, streaky head and neck, a white patch on the hindneck and rump, and bright blue feet. The red-footed booby is smaller, with red feet. The masked and Nazca boobies are white, with dark flight feathers and tail. The brown pelican also plunge-dives, but it’s far bigger, with a huge pouched bill.
It used to be treated as a subspecies of the brown booby. Since 2024 the major North American and world checklists treat the eastern Pacific birds, including those in Baja California, as a separate species, Sula brewsteri.
Yes, all year. It’s the most common booby at the tip of the peninsula, often perched on the rocks around the Arch or diving over bait.
It isn’t on Mexico’s NOM-059 list of species at risk, unlike the blue-footed booby. It is a resident of the Cabo San Lucas protected area, and a hooked or injured bird should be released carefully or reported to PROFEPA.
Top illustration: Top Anglers. Photos: iNaturalist contributors, credited on each photo.
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