Birds
Blue-footed Booby
Sula nebouxii · also called blue-footed booby
The blue-footed booby wears its diet on its feet. The turquoise webbing that makes it a tourist favourite is a live readout of the bird’s health — bright when it is well-fed, faded within two days when it is not — and males flaunt it in a slow, high-stepping courtship parade.
Overview
Blue-footed boobies live along the tropical eastern Pacific, from the Gulf of California to Peru, including the Galápagos. They are plunge-divers, dropping from 10–25 metres onto schools of sardines, anchovies, and flying fish, often in flocks that hit the water together.
Feet that tell the truth
The blue comes from carotenoid pigments in fresh fish that the bird cannot make itself. Because those pigments are also used by the immune system, only a healthy, well-fed booby has enough to spare for bright feet — and the colour fades within about 48 hours of a food shortage. Foot brightness is an honest, real-time fitness signal.
The dance
A courting male lifts each blue foot high in an exaggerated strut, sky-points with bill and wings raised, whistles, and offers a twig. Females prefer brighter feet and invest less in eggs when a partner’s feet are dulled. Having no brood patch, boobies then incubate the eggs by wrapping their warm feet around them.
The name
“Booby” is from Spanish bobo, “clown” — sailors mistook the birds’ fearlessness and waddling dance for stupidity. It is really the mark of evolving on predator-free islands.
Status
The blue-footed booby is Least Concern overall but declining in the Galápagos, where breeding has been poor for years amid a drop in sardines.
Blue-footed Booby: common questions
Why does the blue-footed booby have blue feet?
The colour is a diet-based health signal. The blue and blue-green of the webbing comes from carotenoid pigments that the booby can only get by eating fresh fish; the bird cannot manufacture them. Carotenoids are also used by the immune system, so a booby that is well-fed and healthy has spare pigment to deposit in its feet, while one that is stressed, sick, or short of food diverts those pigments elsewhere and its feet fade — measurably, within about 48 hours of a food shortage. This makes foot colour an honest, up-to-the-minute advertisement of how good a forager and how healthy a bird is, which is exactly the information a potential mate wants.
What is the blue-footed booby's mating dance?
It is a slow, deliberate display built around the feet. The male approaches a female and lifts one brilliant blue foot high off the ground, holds it, sets it down, and lifts the other, exaggerating each step. He punctuates this with "sky-pointing" — throwing his head back, raising his folded wings, pointing his bill straight up, and giving a thin whistle — and by presenting nest material such as a twig or stone. Females judge partners heavily on foot brightness — experiments that painted a male's feet duller made females less interested and led them to invest less in the resulting eggs. Pairs that stay together still re-perform parts of the dance each breeding season.
How did the booby get its name?
From the Spanish "bobo," meaning "fool" or "clown." Early European sailors found these seabirds almost fearless of people — boobies would land on ships and could be approached and caught by hand on their island colonies — and mistook that tameness, plus the birds' comical waddling gait and elaborate dance, for stupidity. In fact the lack of fear simply reflects having evolved on remote islands with no native land predators. The clumsy walk is the trade-off for a body superbly built for plunge-diving and fast flight over open ocean.
How deep and how fast do blue-footed boobies dive?
They typically launch plunge-dives from 10 to 25 metres up, fold their wings back into a tapered arrow shape just before impact, and knife into the water, often only reaching a few metres deep but sometimes continuing to swim down after fish. Diving from that height they hit the surface hard, and boobies have a network of air sacs beneath the skin of the head, neck, and breast that absorb the shock, along with permanently closed external nostrils so water is not forced in. They frequently dive as a group — a flock circling over a fish school will suddenly pour into the sea together, which helps confuse the prey and may reduce each bird's own risk.