Sargasso shearwater

The Sargasso shearwater is on average in length—about half the size of the great shearwater (Puffinus gravis)—and weigh 170 g. There is some variation between populations, and the normal size and weight range is In general appearance, it is a small shearwater, black above and white below and hard to distinguish from its relatives at first glance. 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, and the bill is grey, darker towards the tip, and with a pinkish hue. 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. 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. Its twittering calls and mewing are often only heard at night in the breeding colonies. ==Range and ecology==

The Sargasso shearwater breeds primarily on islands in the Caribbean and Lucayan Archipelago. During the non-breeding season, it ranges across the northwestern Atlantic Ocean, particularly along the Gulf Stream and Sargasso Sea. 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.  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 ==Systematics==

The Sargasso shearwater belongs to the genus Puffinus of mid-sized and small shearwaters. Within Puffinus, the taxonomy of this species has been convoluted. It has traditionally been considered the nominate subspecies of the larger Audubon's shearwater complex, which included up to 10 subspecies. Although of somewhat limited value in procellariiform birds, analysis of mtDNA cytochrome b sequence data indicated that at least three major clades were distinguished within the traditional "Audubon's shearwater" complex. Following further genomic research, the majority of these taxa are now generally considered to comprise their own species, including Sargasso shearwater. The lherminieri clade (Atlantic Ocean, Caribbean) • Sargasso shearwater, Puffinus lherminieri Lesson, 1839 – breeds throughout the Caribbean, on the Bahamas and formerly on Bermuda; ranges throughout the Caribbean and up the North American Atlantic coast up to southern Canada, with vagrants having been recorded off north-eastern Canada. The persicus clade (West Indian Ocean) • Persian shearwater, Puffinus persicus Hume, 1837 – breeds on Khuriya Muriya Islands (Arabian Sea); ranges throughout the Arabian Sea. This group is the most confusing of all. The subspecies dichrous occurs in two areas which appear to be separated by the whole of Indonesia and the seas surrounding it; the Pacific subpopulation includes the proposed subspecies polynesiae (Ta'ū, American Samoa) and possibly gunax (see below), whereas the geographically separated Indian Ocean subpopulation contains the birds formerly separated as nicolae (NW Indian Ocean, from Aldabra to the Maldives) and colstoni (Aldabra, Arabian Sea). . There appear to be no significant genetical or morphological differences between these birds, which is quite amazing given that the Pacific and Indian Ocean subpopulations must have been isolated for a fairly long time, and that no less than three unequivocally distinct subspecies (bailloni, persicus and temptator) occur within the range of Indian Ocean dichrous. On the other hand, the supposed species Mascarene shearwater (P. atrodorsalis) is inseparable morphologically and genetically from bailloni. Clearly, some mechanism blocking gene flow is at work, but what this is exactly remains unknown – though as remarked above, separate breeding seasons seem a reasonable assumption and are tentatively supported by the available field data. been proposed as a distinct species, Bannerman's shearwater (P. bannermani). In the absence of more recent data to investigate this claim, its status continues to be altogether unresolved, though the case for it being at least a distinct subspecies in the bailloni clade seems good. The little-known Heinroth's shearwater (P. heinrothi) was sometimes considered a subspecies of either the Audubon's or the little shearwater complexes. Its actual relationships remain uncertain due to lack of specimens. ==Footnotes==