The Blue booby bird is a marine bird native to subtropical and tropical regions of the Pacific Ocean. The natural breeding habitats of the blue-footed booby are the tropical and subtropical islands of the Pacific Ocean. It can be found from the Gulf of California down along the western coasts of Central and South America down to Peru. Approximately one half of all breeding pairs nest on the Galápagos Islands. Its diet mainly consists of fish, which it obtains by diving and sometimes swimming underwater in search of its prey. It sometimes hunts alone, but usually hunts in groups. It is one of six species of the genus Sula – known as boobies. It is easily recognizable by its distinctive bright blue feet, which is a sexually selected trait. Males display their feet in an elaborate mating ritual by lifting them up and down while strutting before the female. The female is slightly larger than the male and can measure up to 90 cm long with a wingspan of up to 1.5 m.
Its wings are long and pointed and brown in color. The neck and head of the blue-footed booby are light brown with white streaks while the belly and underside exhibit pure white plumage. Its eyes are placed on either side of its bill and oriented towards the front, enabling excellent binocular vision. Its eyes are a distinctive yellow, with the male having more yellow in its irises than the female. Blue-footed booby chicks have black beaks and feet and are clad in a layer of soft white down. The subspecies S. n. excisa that breeds on the Galapagos Islands is larger than the nominate subspecies and has lighter plumage especially around the neck and head.
The Peruvian booby is similar in appearance but has grey feet, whiter head and neck, and white spots on its wing coverts. The ranges of the two species overlap in the waters of northern Peru and southern Ecuador.
Since the blue-footed booby preys on fish by diving headlong into the water, its nostrils are permanently closed, and it has to breathe through the corners of its mouth. Its most notable characteristic is its blue-colored feet, which can range in color from a pale turquoise to a deep aquamarine. Males and younger birds have lighter feet than females. Its blue feet play a key role in courtship rituals and breeding, with the male visually displaying its feet to attract mates during the breeding season.
The blue-footed booby is distributed among the continental coasts of the eastern Pacific Ocean from California to the Galápagos Islands down into Peru. It is strictly a marine bird. Its only need for land is to breed and rear young, which it does along the rocky coasts of the eastern Pacific.
The blue color of the blue-footed booby’s webbed feet comes from carotenoid pigments obtained from its diet of fresh fish. Carotenoids act as antioxidants and stimulants for the blue-footed booby’s immune function, suggesting that carotenoid-pigmentation is an indicator of an individual’s immunological state. Blue feet also indicate the current health condition of a booby. Boobies that were experimentally food-deprived for forty-eight hours experienced a decrease in foot brightness due to a reduction in the amount of lipids and lipoproteins that are used to absorb and transport carotenoids. Thus, the feet are rapid and honest indicators of a booby’s current level of nourishment. As blue feet are signals that reliably indicate the immunological and health condition of a booby, coloration is favored through sexual selection.