Sula di Abbott

Identificazione

Abbott's booby is the largest of all booby species, and is adapted to long-distance flight. Individuals can reach 80 cm (31 in) from beak to tail, and weigh about 1.5 kg (3.3 lb). It is distinguished from other sulids in the region by its black and white plumage; the only other bird with similar coloration and shape is the masked booby, which has an all-white body with black wings only. They have an off-white plumage, which contrasts with black eye patches, black wings and tails, and black flank marks. Their feet are blue and webbed, with black outer ends. Males have pale grey bills with a black tip, whereas females have pink bills with a black tip. Chicks have white down and a cape of black scapular feathers.<p>Juvenile birds have plumage similar to adults, unlike other species of boobies.

Tassonomia

The first specimen was collected from Assumption Island in 1892 by American naturalist William Louis Abbott, northwest of Madagascar, although debate exists as to whether he actually collected it from the nearby Glorioso Island. It was described by Robert Ridgway in 1893. In 1988, it was placed in its own genus by Olson &amp; Warheit 1988. The basal characters present in this species suggest it may be an early branch of the sulid family, antedating the split between gannets and other boobies. This was reinforced by analysis of the mitochondrial cytochrome b gene in 1997, which indicated Abbott's booby was an early offshoot of the gannets rather than the other boobies. However, 2011 study of multiple genes found it to be basal to all other gannets and boobies, and likely to have diverged from them around 22 million years ago. A subfossil subspecies from the Mascarene Islands of Mauritius and Rodrigues was named P. a. nelsoni in 2023.

Nome scientifico

Papasula abbotti

Autorità

(Ridgway, 1893)

Ordine

Suliformi

Famiglia

Sulidae

Genere

Papasula

Areale e habitat

Abbott's booby is the only booby restricted to a single location, although its former distribution covered much of the Indian and Pacific Oceans. Fossil evidence indicates its former presence in the South Pacific, and eyewitness reports of it formerly breeding on the Mascarene Islands. In April 2007, an individual of this species was photographed at a booby colony on Rota in the Pacific Ocean, and the same individual has been seen off-and-on in the red-footed booby colony there through at least 2024.<p>It breeds in tall trees in the plateau forests of the central and western areas of Christmas Island, and in the upper terrace forests of the north coast. Nest distribution is patchy, based on topography, with the majority of nests in trees on uneven terrain. Nests are usually built on Syzygium nervosum and Planchonella nitida trees, although emergent Tristiropsis acutangula trees are sometimes used. Due to the trade winds flowing south-east from April to November, trees that can be approached from the northwest are favoured.<p>Its foraging range usually reaches 40–100 km (25–62 mi) from Christmas Island, although individuals are often seen in Indonesia and vagrants reach as far as mainland Australia. A single female was recently observed on Rota, northeast of Guam in the Pacific, and some records from the Banda Sea indicate either an even larger range or unknown breeding colonies.

Areale riproduttivo

IO : Christmas I. (s of w Java); formerly Assumption (Aldabra group, sw Seychelles), Mauritius and Rodrigues (c, e Mascarenes, sw Indian Ocean); subfossil remains from Solomon Is., Vanuatu, and Marquesas (ne Polynesia)

Areale non riproduttivo

to near Java, s, c Moluccas and sw of New Guinea

Migrazione

Complete migrants

Comportamento

Individuals are solitary, long-distance travellers that can range thousands of kilometres from Christmas Island. They are very vocal, with a wide range of calls. Due to their size, they require a large clear space to take off. So, they nest near the tops of trees. If an individual falls to the forest floor, it will starve unless it can climb high enough to be able to catch the wind and take off. Adults rarely fight owing to the risk of falling. Fledglings must succeed in their first attempt at flight; unsuccessful attempts rarely result in the fledgling's survival.<p>Adults forage at sea from October to April, although they return if they have a chick that is dependent on them. They forage in offshore waters, eating fish and squid. No feeding patterns are known, although they are thought to forage in an ocean upwelling off Java, 300 km (186 mi) northwest of Christmas Island. Chicks are fed through complete regurgitation for the first two weeks, then incomplete regurgitation. Both parents feed the young.<p>Courtship takes the form of a face-to-face display. Partners mate for life, and maintain the same nest site throughout their lives. Nests are made near the top of rainforest trees, 10–40 m (33–131 ft) off the ground, usually at elevations of 150 m (492 ft) or higher. Breeding cycles last 15–18 months, and only one egg is laid during each cycle. Successful pairs can nest once every two years, but often take rest years between attempts to raise a chick. These rest years are taken even if the couple is unsuccessful in raising their chick. Most pairs only breed once every three years.<p>Mating usually takes place in April, and eggs are laid between April and July. Eggs are equal to 8% of the female's body weight. They are incubated under the webbed feet of the parents, which become vascularised and warm. Incubation is undertaken by both parents, which take shifts of up to two days. Eggs are incubated for about 56 days, which is 30 days longer than in other sulids. Chicks hatch from June to November, after the eggs are incubated around 56 days. They take 170 days to fully fledge, and an additional 200 days to become fully independent. Most chicks make their first flight in December or January. Fledglings reach maturity around eight years of age, and can live up to 40 years.

Conservazione

Tendenza della popolazione

stable