English Name: Audubon's Shearwater
Scientific Name: Puffinus Iherminieri
Audubon's Shearwater, Puffinus lherminieri, is a common tropical seabird from the family Procellariidae. Sometimes called Dusky-backed Shearwater[1], the scientific name of this species commemorates the French naturalist Félix Louis L'Herminier.
Certain populations are also known as Baillon's Shearwater or Tropical Shearwater, Bannerman's Shearwater, Mascarene Shearwater and Persian Shearwater; some of these are considered distinct species by various authors[1]. If they are all placed in P. lherminieri, the North Atlantic Little Shearwater (otherwise often separated as P. baroli) is generally included here too. Thus, these small shearwaters form a cryptic species complex.
Description
Audubon's Shearwaters are on average 30 cm (12 in) in length—about half the size of the Greater Shearwater ("Puffinus" gravis)—and weigh 170 g. There is some variation between populations and the normal size and weight range is 27[verification needed]–33 cm and 150–230 g. The wingspan is 64–72 cm, the tail is around 8.5 cm long, the exposed culmen measures 3 cm or slightly less, and the tarsus is around 4 cm in length.[2] In general appearance, it is a small shearwater, black above and white below and hard to distinguish from its relatives at first glance.[1]
The upperparts, rectrices and undertail coverts are blackish-brown, as are at least the distal undersides of the remiges, but sometimes the entire feathers. The rest of the underparts are white, as is the head below eye level. The iris is dark, the feet are dull pink with a black wash and black toenails[2], and the bill is grey, darker towards the tip, and with a pinkish hue.[1]
Males and females look alike. Immature birds do not have a distinct plumage, while the nestlings are covered with down feathers, grey above and whitish on the belly.[1]
It can be confused with the Manx Shearwater (P. puffinus), which has white undertail coverts and in direct comparison a longer bill. Other similar-looking species are usually completely allopatric, though the largely subantarctic Little Shearwater (P. assimilis) may occasionally range into waters where P. lherminieri is normally found. It has more white on the face and underwing, a smaller bill and greyish-blue feet.[1]
Its twittering calls and mewing are often only heard at night in the breeding colonies.
Range and ecology
If not split into several species, Audubon's Shearwater ranges across the Indian Ocean north to the Arabian Sea, throughout the northwest and central Pacific, in the Caribbean, and parts of the eastern Atlantic. It is a species of tropical waters; only some Atlantic populations and Bannerman's Shearwater of the Ogasawara Islands occur farther north. Unlike the larger shearwaters, adult Audubon's Shearwaters are not thought to wander much or undertake great migrations, although their young birds do so before breeding, and western Indian Ocean birds may gather in large numbers at the upwelling zone in the Arabian Sea.[1]
It is adaptable as regards its preferred marine habitat; it can be found in pelagic, offshore and inshore waters. It feeds in a variety of methods, mainly diving out of flight, plunging underwater from a swimming position, and picking up food less than a bill's length underwater while "pattering" as if it were walking across the waves. It eats small fish, squid and planktonic crustaceans. Unlike other shearwaters, it is not commonly a ship-follower, though it may attend small fishing boats; it is also sometimes met with as part of a mixed-species feeding flock. [1]
The species is colonial, nesting in small burrows and crevices in rocks and on earthy slopes on atolls and rocky islets. The breeding season varies according to location and subspecies, but how precisely is not very well-studied[3]. Both parents share the responsibility of incubating the single white egg (measurements of 52.5 by 36.2 mm and a weight of 37 g have been recorded for one specimen of average size[2]), each incubating for periods of 2 to 10 days until the egg hatches after 49-51 days of incubation. The nestlings are brooded for half a week to one week, after which time the parents will leave it mostly alone in the burrow and spend most of their time foraging and feeding their voracious offspring, which become very fat. Time from hatching to fledging is 62-75 days. Audubon's Shearwaters take about 8 years to reach breeding age. As typical for Procellariiformes they are long-lived for their size, one bird ringed as an adult was still alive 11 years later; it must have been more than 15 years old at that time.[1]
While some small populations are threatened, the species as a whole (in the present sense, i.e. unsplit) is not considered to be globally threatened.[4]
Systematics
Audubon's Shearwater belongs to the Puffinus sensu stricto group of mid-sized and small shearwaters, which is related to the genus Calonectris. The taxonomy of this species is extremely confusing. It is occasionally listed as a subspecies of P. assimilis (the Little Shearwater), but they do not appear to be that closely related. Rather, P. lherminieri seems to belong to an ill-resolved clade also including such species as the Little Shearwater, the Manx Shearwater (P. puffinus) or the Black-vented Shearwater (P. opisthomelas).[5]
The little-known Heinroth's Shearwater (P. heinrothi) is sometimes considered a subspecies of either Audubon's or the Little Shearwater. Though it is likely to be another member of that close-knit group, its actual relationships remain uncertain due to lack of specimens.
Audubon's Shearwater itself has around 10 subspecies. Several have at one time or another been suggested to constitute separate species. For example, the Galápagos Islands population has turned out to be a very distinct species, the Galápagos Shearwater (P. subalaris); it is apparently related to the Christmas Shearwater (P. nativitatis) and together with it constitutes an ancient lineage without other close relatives in the genus. Other taxa were initially assigned to the Little Shearwater and later moved to Audubon's. Analysis of mtDNA cytochrome b sequence data[7] – which is of somewhat limited value in procellariiform birds however
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