The Audubon's Shearwater, Puffinus lherminieri, also known as the Tropical Shearwater, is a common seabird of the tropics from the family Procellariidae. The scientific name commemorates the French naturalist Félix Louis L'Herminier.
Audubon's Shearwater ranges (depending on the taxonomical status, see below) 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 the Atlantic populations and Bannerman's Shearwater of the Ogasawara Islands occur farther north.
The adults are not thought to wander or undertake great migrations like other members of the genus Puffinus, although young birds do so before breeding. The species is colonial, nesting in small burrows and crevices in rocks. Both parents share the responsibility of incubating the single egg, taking stints of between 2 to 10 days. The egg takes about 50 days to hatch, and another 70 days to rear to fledging. Once fledged a chick will take 8 years to reach breeding age. Like other shearwaters they are long lived, one bird ringed as an adult was caught again 11 years later.
The Audubon's Shearwater can reach 30 cm. (12 in.) long and weigh up to 170 g, about half the size of the Greater Shearwater. The upperparts and the undersides of the tail and flight feathers are blackish-brown, and the rest of the underparts, cheeks and throat are white. It can be confused with the Manx Shearwater which has white undertail covers.
Audubon's Shearwater chick on Little Tobago.
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, both diving below the surface to chase prey, pursuit plunging, and surface feeding. It takes small fish, squid and crustaceans. Unlike other birds of the genus, it is not a ship follower. Its twittering calls and mewing are often only heard at night in the breeding colonies.
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.
Audubon's Shearwater belongs to the Puffinus sensu stricto group of mid-sized and small shearwaters. The taxonomy of this species is extremely confusing. It is occasionally listed as a subspecies of the Little Shearwater, but they do not appear to be very closely related (Austin 1996, Heidrich et al. 1998, Austin et al. 2001). The little-known Heinroth's Shearwater is sometimes considered a subspecies of either species; 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 (Puffinus subalaris); it is apparently related to the Christmas Shearwater and together with it constitutes an ancient lineage without other close relatives in the genus (Austin et al. 2004). Other taxa were initially assigned to the Little Shearwater and later moved to Audubon's. Analysis of mtDNA cytochrome b sequence data (Austin 1996, Austin et al. 2004), which is of somewhat limited value in procellariiform birds however (Rheindt & Austin 2005), indicates that at least 3 major clades can be distinguished:
lherminieri clade (Atlantic Ocean, Caribbean)
- P. l. lherminieri (Caribbean)
- P. l. baroli (Azores and Canary Islands, E Atlantic)
- P. l. boydi (Cape Verde Islands, E Atlantic)
The latter two were formerly placed in the Little Shearwater (Austin 1996, Heidrich et al. 1998) and are considered a distinct species (North Atlantic Little Shearwater, P. baroli) by some, depending on whether biogeography and morphological differences, or the genetic similarity are considered more significant. The southern Caribbean birds were separated as P. l. loyemilleri, but are not distinct (Austin et al. 2004).
- P. l. persicus (Kuria Muria Island, Arabian Sea)
- P. l. temptator (Mohéli/Mwali, Comoros)
These form another distinct clade as indicated by mtDNA sequences, and have for some time been proposed as a distinct species, Persian Shearwater (P. persicus). From the molecular data alone, this seems fairly warranted, but the ranges of the two taxa are quite far apart, separated by forms of the third clade. It is quite obvious that on the basis of such contradicting data as presently available, no decision can be taken regarding the taxonomic status of these birds. Possibly, they do form a distinct species separated from the third clade by a different circannual rhythm, as is known from other procellariiform birds. If P. bailloni is accepted as a distinct species but P. persicus is not, these subspecies would have to be transferred to the Tropical Shearwater (Austin et al. 2004).
- P. l. bailloni (Mascarene Islands)
- P. l. dichrous (Polynesia and NW Indian Ocean up to Arabian Sea; possibly Melanesia)
This group is the most confusing of all. The supposed species Mascarene Shearwater ("P. atrodorsalis") is inseparable morphologically and genetically from bailloni.
The subspecies dichrous occurs in two areas which appear to be separated by the whole of Indonesia; the Pacific subpopulation includes the proposed subspecies polynesiae (Taumanua, 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 Maledives) 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. 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: Carboneras 1992). In addition, it is entirely mysterious why such a mechanism should apply in the rather limited and ecologically homogenous northwestern Indian Ocean range, but not in the ecologically more diverse and by far larger Pacific range of dichrous.
These unresolved problems nonwithstanding, this clade - possibly including the preceding one - has been proposed to constitute a separate species, the Tropical Shearwater or Baillon's Shearwater, Puffinus bailloni (Austin et al. 2004).
- P. l. gunax (Banks Islands, Vanuatu)
- P. l. bannermani (Ogasawara Islands, NW Pacific)
These taxa could not be included in the most recent studies due to lack of material. The case of gunax seems fairly straightforward - as certainly as this can possibly be said in the absence of new data, it belongs to the bailloni clade either as a distinct subspecies, or, more likely, as yet another synonym of dichrous.
The case of the more distinct bannermani, the range of which is parapatric to that of the Pacific dichrous, is more complicated. It has for some time (Vaurie 1965) 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.