Sulids are the gannets and boobies, streamlined seabirds built for one of the most spectacular feeding methods in nature: the plunge dive. The blue-footed booby pictured is 32 inches (81 cm) long with a 5-foot (1.5 m) wingspan and weighs 3.3 lbs (1.5 kg). The northern gannet, the largest sulid, is 3 feet (1 m) long with a 6-foot (1.8 m) wingspan.
They have long, pointed wings, a wedge-shaped tail, a dagger bill and forward-facing eyes for judging distance. There are no external nostrils, and air sacs under the skin of the face and chest cushion the impact of hitting the water at 60 mph (100 km/h).
The blue-footed booby's feet really are blue, coloured by pigments from its fish diet, and the bluer the feet, the healthier the bird.
Gannets live in cool northern and southern seas: the northern gannet in the North Atlantic, the Cape gannet off South Africa and the Australasian gannet around Australia and New Zealand. Boobies live in the tropics around the world. The blue-footed booby breeds from the Gulf of California to Peru and especially on the Galapagos Islands.
All nest in colonies on islands and cliffs; Bass Rock in Scotland holds the largest gannet colony on Earth.
Sulids eat schooling fish such as sardines, anchovies, mackerel and flying fish, along with squid. Spotting prey from the air, they fold their wings and plunge from up to 100 feet (30 m), piercing the water like arrows and sometimes swimming further down with their wings. Whole flocks dive together into a shoal in a storm of white splashes.
Blue-footed boobies are famous for their courtship dance, in which the male lifts his blue feet one at a time, spreads his wings and points his bill to the sky while whistling. Gannets greet each other with bill-fencing and sky-pointing too.
Sulids nest in tightly packed colonies and lay one to three eggs, keeping them warm under their webbed feet, which are laced with blood vessels. Sailors named the boobies for their tameness, from the Spanish bobo, a clown or fool.
The family Sulidae contains three gannets and seven boobies. The IUCN lists the blue-footed booby and the gannets as Least Concern, though the Galapagos blue-footed population has fallen as sardines have declined. Abbott's booby, which nests only on Christmas Island, is Endangered.
Avian flu swept through northern gannet colonies in 2022, and overfishing of forage fish, oil spills and plastic in nests are continuing threats.
