Gannets and boobies spear the sea from midair colonies
Sulidae's eleven gannet and booby species are medium-large coastal plunge-divers, split morphologically and genetically between Sula boobies and Morus gannets. Bodies run about sixty to eighty-five centimeters with wingspans near 140–175 centimeters, four-toed webs, and serrated bills that hinge for big prey.
Gannets and boobies are shaped for hitting water at speed. Their flight muscles are relatively small, trading some flying ability for a slim, torpedo-like body with little drag. Nostrils open inside the bill rather than to the outside, keeping water out during a plunge, and forward-facing eyes give a wider field of binocular vision than most birds have. The long, saw-edged bill has an upper mandible that can flex upward to take large prey. A dive carries the bird one to two metres under, and if a fish escapes it chases with wings and feet.
Unlike their cormorant and darter relatives, sulids have a well-developed preen gland and spread its waxy oil on their feathers for waterproofing. They replace wing feathers in stages, so from the first moult onward they always carry a mix of old and new plumage. All four toes are joined by webbing, which some species colour brightly for courtship.
Breeding happens in colonies. Males pick and defend nest sites, then court with head-shaking displays, and pairs keep their bond by preening each other. They have no brood patch; instead their webbed feet fill with blood and grow warm, and the parents incubate the usually two eggs beneath them for 42 to 55 days. Rarely does more than one chick survive, except in the Peruvian booby, which lays two to four.
The 11 species fall into three genera: six Sula boobies, three Morus gannets, and Abbott's booby in Papasula. A 2011 genetic study found Abbott's booby split from the rest about 22 million years ago, while the gannets diverged from each other only about 2.5 million years ago. Sulids form the oldest branch of a group with the cormorants and darters, now often placed in the order Suliformes.
Source: Sulidae
