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Jun 25, 2017 Features / Columnists, Interesting Creatures in Guyana
The blue-footed booby (Sula nebouxii) is a marine bird native to subtropical and tropical regions of the Pacific Ocean. 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 (35 in) long with a wingspan of up to 1.5 m (5 ft).
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.
The blue-footed booby usually lays one to three eggs at a time. The species practices asynchronous hatching, in contrast to many other species whereby incubation begins when the last egg is laid and all chicks hatch together. This results in a growth inequality and size disparity between siblings, leading to facultative siblicide in times of food scarcity. This makes the blue-footed booby an important model for studying parent-offspring conflict and sibling rivalry.
The blue-footed booby is on average 81 cm (32 in) long and weighs 1.5 kg (3.3 lb), with the female being slightly larger than the male. 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.
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-coloured 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.
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.
A booby may use and defend two or three nesting sites, which consist of bare black lava in small divots in the ground, until they develop a preference for one a few weeks before the eggs are laid. These nests are created as parts of large colonies.
While nesting, the female will turn to face the sun throughout the day, so the nest is surrounded by excrement.
Females start breeding when they are one to six years old, while males start breeding when they are two to six years old. There is very limited natal dispersal, meaning that young pairs do not move far from their original natal nests for their own first reproduction, leading to the congregation of hundreds of boobies in dense colonies.
The benefit of limited dispersal is that by staying close to their parents’ nesting sites, the boobies are more likely to have a high quality nest. Since their parents had successfully raised chicks to reproductive age, their nest site must have been effective, either by providing cover from predation and parasitism, or by its suitability for taking off and landing. Bigamy has been observed in the species, and there are known cases where two females and one male all share a single nest.
The blue colour 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 favoured through sexual selection.
The blue-footed booby’s is a specialized fish eater, feeding on small schooling fish such as sardines, anchovies, mackerel, and flying fish. It will also take squid and offal. The blue-footed booby hunts by diving into the ocean after prey, sometimes from a great height, and can also swim underwater in pursuit of its prey. It can hunt singly, in pairs, or in larger flocks. Boobies travel in parties of about 12 to areas of water with large schools of small fish. When the lead bird sees a fish shoal in the water, it will signal to the rest of the group and they will all dive in unison, pointing their bodies down like arrows.
Plunge diving can be done from heights of 10–30.5 m (33–100 ft) and even up to 100 m (330 ft). These birds hit the water around 97 km/h (60 mph) and can go to depths of 25 m (82 ft) below the water surface. Their skulls contain special air sacs that protect the brain from enormous pressure.
Prey are usually eaten while the birds are still underwater. Surprisingly, individuals prefer to eat on their own instead of with their hunting group, usually in the early morning or late afternoon. Males and females fish differently, which may contribute to why blue-foots, unlike other boobies, raise more than one young. [Source: Wikipedia]
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