| Red-footed booby | |
|---|---|
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| White morph,Philippines | |
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| Brown morph, male,Galápagos Islands | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Suliformes |
| Family: | Sulidae |
| Genus: | Sula |
| Species: | S. sula |
| Binomial name | |
| Sula sula | |
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| Synonyms | |
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Thered-footed booby (Sula sula) is a largeseabird of thebooby family,Sulidae. Adults always have red feet, but the colour of theplumage varies. They are powerful and agile fliers, harnessing the wind to fly efficiently,[4] but they are clumsy in takeoffs and landings. They forage by catching flying fish from above the ocean's surface[5] and by performing shallow dives.[6] They are found widely in the tropics, and breedcolonially in coastal regions, especially isolated islands such asSt. Brandon,Mauritius (Cargados Carajos shoals), and the Chagos Archipelago. Although its population is declining, it is considered to be aleast-concern species by theInternational Union for Conservation of Nature (IUCN). It faces threats from climate change, competition with fisheries, human disturbance, and invasive species.
The red-footed booby wasformally described by the Swedish naturalistCarl Linnaeus in 1766, in thetwelfth edition of hisSystema Naturae. He gave it thebinomial namePelecanus sula and described it based on a specimen fromBarbados.[7][8][9] The present genusSula was introduced by the French scientistMathurin Jacques Brisson in 1760.[10] The wordSula is Norwegian for agannet.[11]
There are three subspecies:[12]
The red-footed booby is the smallest member of thebooby and gannet family at about 70 cm (28 in) in length and with awingspan of up to 152 cm (60 in).[13] The average weight of 490 adults fromChristmas Island was 837 g (1.845 lb).[14] It has red legs, and itsbill and throat pouch are coloured pink and blue. This species has severalmorphs. In the white morph theplumage is mostly white (the head often tinged yellowish) and theflight feathers are black. The black-tailed white morph is similar, but with a black tail, and can easily be confused with theNazca andmasked boobies. The brown morph is overall brown. The white-tailed brown morph is similar, but has a white belly, rump, and tail. The white-headed and white-tailed brown morph has a mostly white body, tail and head, and brown wings and back. The morphs commonly breed together, but in most regions one or two morphs predominates; for example, at theGalápagos Islands, most belong to the brown morph, though the white morph also occurs.
The sexes are similar, and juveniles are brownish with darker wings, and pale pinkish legs, while chicks are covered in dense white down.
The red-footed booby is widespread throughout the tropics of the Atlantic, Pacific, and Indian Oceans. In the Atlantic, they mainly live in theCaribbean islands.[15] In the Pacific, populations can be found in theGalapagos Islands, mostly onGenovesa andSan Cristobal[16] and inHawaii, onKauai.[17] In the Indian Ocean, it is found onAldabra, theSeychelles,Rodrigues, theMaldives, theChagos Archipelago, theCocos (Keeling) Islands, andChristmas Island.[18]
The red-footed booby has beenextirpated from a large number of islands due to a combination of introduced predators and human predation, including theGlorioso Islands,Assumption Island,Tikopia,Henderson Island, theMarquesas Islands, theSociety Islands, andDesecheo Island.[18] The species is avagrant toSri Lanka,[19] New Zealand,[20] and the United Kingdom.[21]
This species breeds on islands in most tropical oceans. When not breeding it spends most of the time at sea. In the Chagos Archipelago, it remains close to its breeding colony throughout the year, rather than migrating.[22] It nests in large colonies, laying one chalky blue egg in a stick nest, which is incubated by both adults for 44–46 days. The nest is usually placed in a tree or bush, but rarely it may nest on the ground. It may be three months before the young first fly, and five months before they make extensive flights.
Red-footed booby pairs may remain together over several seasons. They perform elaborate greeting rituals, including harsh squawks and the male's display of his blue throat, also including short dances.
The diet of red-footed boobies consists mostly offish (such asExocoetidae flying fish andGempylidae escolars) andsquid.[23] Studies of the red-footed booby onChristmas Island have found that most fish eaten are 6–15 cm (2.4–5.9 in) long, with a maximum length of 20 cm (7.9 in), and most squid are 6–10 cm (2.4–3.9 in), with a maximum length of 15 cm (5.9 in). OnAldabra, the proportion of fish and squid in the diet varies between seasons; squid make up 21% of the diet by mass in the wet season and 1% in the dry season. They generally catch prey by diving into the ocean vertically from heights of 4 to 8 m (13 to 26 ft), although flying fish may be caught while in the air, as evidenced via bird-borne video footage.[18][24] Red-footed boobies travel hundreds of kilometers from land when they are foraging for prey, and sometimes engage in multi-day trips.[25]
Adult red-footed boobies are known to be hunted bycoconut crabs; the crabs use their powerful claws to break the wings of boobies or catch them by their legs. One booby attacked while asleep on a low branch was killed by six coconut crabs over a period of several hours, while another caught after landing near the entrance to a crab burrow was dragged inside.[26] Red-footed booby nestlings and eggs are also attacked by a variety of predators, including rats, cats, pigs,[18] raptors,[27] andMicronesian starlings,[28] although introduced mammalian predators have a limited impact as the booby nests in trees.[18] However, the booby's habit of breeding on remote islands may be an adaptation to avoid predation;[18] on theGalápagos Islands, the red-footed booby does not nest on any islands inhabited by theGalapagos hawk, even when they have suitable conditions, and has been observed colonizing islands soon after the hawk isextirpated on them.[29] Humans eat both red-footed booby adults and nestlings; boobies will bite humans trying to catch them near their nest.[18]
Parasites recorded from the species include the tickOrnithodoros capensis in nests and thebird lousePectino pygus in adults.[18]
TheInternational Union for Conservation of Nature (IUCN) lists the red-footed booby as a species ofleast concern, though the population worldwide is decreasing.[2] The warm phase (El Niño) of theEl Niño–Southern Oscillation in 1982 and 1983 negatively affected breeding on Christmas Island as higher water temperatures reduced food supply. Where usually 6000 pairs nested, 30 pairs and around 60 pairs attempted breeding in 1982 and 1983 respectively.[30]
