Sula sula
red-footed booby

Red-footed boobies are found in tropical and sub-tropical waters across the globe (they are found in the Oriental, Ethiopian, Neotropical, and Australian regions; they are also found on oceanic islands). They take long hunting trips of up to 150 km from their breeding grounds but do not migrate. One of the largest populations is on the Galapagos Islands. (Alten, 1998; del Hoyo, Eliott, and Sargatal, 1992; eNature.com, 2002)

Red-footed boobies make their nests in the tops of trees on islands and coasts in tropical regions. They may also nest in low scrub. They inhabit islands and coastal regions in the tropics, because they prey on fish in pelagic regions of the ocean. (Alten, 1998; del Hoyo, Eliott, and Sargatal, 1992; eNature.com, 2002; Raikow, 2004)

Sula sula is the smallest booby, and is well suited for its long flights out to sea in search of prey. It has strong neck muscles, and a wedge-shaped tail. It has a long, tapering bill with serrated cutting edges to help catch and eat its prey. Its external nostrils are closed to allow for plunge-diving, but it has developed secondary nostrils beside the mouth which are automatically covered by flaps when it plunges. The skin around its face is generally bare. The eyes are beside the bill, face forward, and have very pale irises. The wings are long, pointed, and situated fairly far back on the body. They help the bird to fly in high winds (which it does by alternating powerful flaps with gliding) and also to dive. When diving, the wings close around the body of the bird, making it more aerodynamic. The legs are short and strong, and the feet are large and totipalmate (webbed between all four toes). The feet are highly vascular because it is through the feet that heat is transmitted from the parent to the offspring. The legs are set far back on the body, helping it to swim. The feet and legs are also red, thus giving the bird its name. Sula sula is very buoyant, having developed a series of air-sacs which are extensions of the bronchi. They help in its plunge-diving.

The plumage of Sula sula must serve two purposes, camouflage and body temperature maintenance. The underpart of the bird is generally white, so as to provide countershading to help prevent its prey from seeing it. Also, "in an environment where both salt and the sun intensify the effects of feather abrasion, dark, melanin-rich feathers on the upper parts help to provide stronger resistance" (del Hoyo et al., 1992). The plumage is molted continuously so as not to hinder the bird's flight capability at any one time, however, molt is suspended during breeding. Feathers are renewed 1 to 2 times yearly. Sula sula lacks a brood patch because it would interfere with streamlining and insulation. There are several morphs of this bird, often making it difficult to identify without noting the color of its feet. The morphs are: the white-tailed brown morph, the white headed and white tailed brown morph, the white morph (which has black on its wings), the black-tailed white morph (found on the Galapagos Islands), and the golden white morph (found on the Christmas Islands).

Red-footed boobies are 70 to 71 cm long, on average and have a wingspan of 91 to 101 cm. They weigh from 900 to 1003 g. Females tend to be slightly larger than males. (Alten, 1998; del Hoyo, Eliott, and Sargatal, 1992; eNature.com, 2002; Raikow, 2004)

Red-footed boobies live as sexually reproductive adults for approximately 23 years but can live for more than 40 years.

Red-footed boobies are highly social birds, and as such have developed highly ritualized behaviors. They have colonial nesting grounds, with as many as several hundred pairs in one location. They can breed in mixed colonies, living with other Sulids. They are mostly diurnal, but have also been known to hunt nocturnally when squid come to the surface of the water. Feather care, particularly oiling, is important as it prevents waterlogging and helps with heat retention. This "involves a bird impregnating its plumage with the waterproofing secretion produced by the preen gland at the base of its tail" (del Hoyo et al., 1992). Other heat regulating methods include exposing the webs of the feet and possibly excreting on them for evaporative cooling. Another method of heat loss is for the bird to hang its wings away from its body to increase its surface area and allow more heat to escape from its body. In order to retain/acquire heat, the bird may sun itself with its wings spread, to allow the dark feathers to absorb heat. The fishing trips that it takes out to sea may last for several days, as it flies farther out than any other Sulid. It may also follow ships out, and use them to perch. (Alten, 1998; del Hoyo, Eliott, and Sargatal, 1992)

Home Range

We do not have information on home range for this species at this time.

There are a variety of calls used by red-footed boobies. Male and female calls are different, due to structural differences in the trachea and syrinx. The male produces mild, plaintive whistles while the female produces trumpeting honks or quacks. The juveniles sound like females. The posturing that is typically used in courtship is also a form of communication. (del Hoyo, Eliott, and Sargatal, 1992)

Sula sula preys on fish. It is known to hunt up to 150 km out to sea, much farther than other Sulids. It plunge-dives to moderate depths (approximately 4 to 10 m) in order to acquire fish, which it catches and swallows on its return to the surface. Red-footed boobies can fly higher than other Sulids (10 to 30 m) when searching for food because of their binocular vision. Once prey are sighted, the bird will dive straight down into the water, reaching its top speed just before entry. The larger females can often catch food that is deeper than the smaller males because of their weight. Sometimes it will also use its wings to swim deeper underwater (15 to 20 m) to reach prey. Red-footed boobies can also catch prey in midflight, due to their smaller size and better agility than other species of booby. This is a particularly effective method for hunting flying fish as they jump out of the water. They are also known to hunt squid at night, as their large eyes allow effective nocturnal hunting. Red-footed boobies are communal hunters and once one bird has spotted food, all will dive. The food is swallowed before the bird emerges from the water; this prevents other individuals from stealing it.

Two favorite foods of red-footed boobies are flying fish, which they are often able to catch in midflight, and squid (that they catch during night hunting). However, they will eat whatever fish are available. (Alten, 1998; del Hoyo, Eliott, and Sargatal, 1992; eNature.com, 2002)

Due to the fact that this particular bird lives in isolated oceanic areas, and often spends much of its time very far from land, it does not have many predators.

Red-footed boobies play an important role in their ecosystem; they have an impact on the fish that they prey on. They do not interact with many other organisms, as they live in such isolated marine areas, often staying far out to sea. (Alten, 1998)

There are no known adverse affects of red-footed boobies on humans.

In some areas people rely on red-footed boobies as a food source. In the past, people who hunted them were always aware of the detrimental effects of their hunting, and as such were cautious not to overhunt the populations. Today, people collect sulids and their eggs and sell them across the world. This has gotten out of control and the exploitation has become a concern.

Conservation parks have been established so that people can visit and enjoy these birds without harming them. (del Hoyo, Eliott, and Sargatal, 1992)

Sula sula is not globally threatened, because it is so widely dispersed. It is one of the most abundant and widespread of all the Sulids. Despite this, the population size has been decreasing steadily over recent centuries. The biggest threats to these birds are deforestation and the fishing industry. Because they live in trees, deforestation destroys their habitat/nesting grounds, and the fishing industry depletes their food source.

While they are not threatened on a global level, in some areas human pressure on their habitats is threatening specific populations. In addition, people collect sulids and their eggs and sell them across the world. This has gotten out of control and the exploitation has become a concern. Red-footed boobies are protected in some areas now. Conservation parks have been set up so that people can visit and enjoy these birds without harming them. Red-footed boobies are protected under the US Migratory Bird Treaty Act. (Alten, 1998; del Hoyo, Eliott, and Sargatal, 1992)

It has been proposed that the name "booby" comes from the spanish word "bobo" meaning stupid or dunce and refers to the bird's characteristic lack of fear of man.