'Southern' Shearwaters Ardenna sg Ardenna & Hemipuffinus

Subgenera Ardenna and Hemipuffinus

Three supposedly closely related species:

Genus Ardenna

Subgenus Ardenna

One species:

Great Shearwater Ardenna gravis

Genus Ardenna

Subgenus Hemipuffinus

Two species are recognized presently:

Pink-footed or Pale-footed Shearwater Ardenna (creatopa) creatopa
Flesh-footed Shearwater Ardenna (creatopa) carneipes

Evolution and taxonomy

After the establishing of the genus Puffinus Mathews & Iredale (1915) proposed a division of Puffinus into several different genera of wich some got the status of subgenus in a later stage. The Great Shearwater P. gravis was assigned to Ardenna and the Pink-footed Shearwater P. creatopus (including carneipes as a subspecies) to Hemipuffinus. These two subgenera were nevertheless considered to be closely related. Later the two subspecies of P. creatopus were separated into two separate species: P. creatopus in the eastern Pacific and P. carneipes in the Australian and New Zealand region. Subsequently P. carneipes was devided into two subspecies: carneipes and hullianus. The latter decision was not generally accepted and usually considered invalid (Brooke 2004).
Recent DNA research (Penhallurick & Wink 2004) suggests that Ardenna gravis and Ardenna creatopa/carneipes are splits from an evolutionary lineage that contains all larger shearwaters of the southeren hemisphere. This lineage diverged from the other shearwaters about 10.4 mya. Bourne (1962) supposed gravis, creatopa and carneipes are to be considered being a circumpolar superspecies.
Penhallurick & Wink proposed to re-establish the genus Ardenna for all larger southern shearwaters, including gravis, carneipes (with creatopa as a pale morph in an East-West cline with subspecific status), bulleri, pacifica, grisea and tenuirostris. This is widely accepted presently but there is still no full agreement on this.

Distribution

A. gravis occurs only in the Atlantic (some vagrants in the Pacific area have taken the wrong turn at Cape Horn). It breeds at Tristan da Cunha and the Falklands. After the breeding season hundreds of thousands of birds migrate to the North Atlantic and follow an eight-shaped route along Ireland and North and South America. The all dark brown A. c. carneipes is at home in the New Zealand and Australian sector and migrates into the western Pacific up to Japanese waters and Indian Ocean. The paler A. c. creatopa breeds on Robinson Crusoe Island and Santa Clara (Juan Fernandez Archipelago) and Mocha Island off Chile and migrates in the eastern Pacific along the American coast to US West Coast waters and even up to Alaska.
See also the Pink-footed Shearwater website.

Behaviour

The two Hemipuffinus species' way of flying resembles much the habits of Calonectris, a rather lazy laboured flight with a few shallow wing beats followed by a glide. In strong winds more shearwatering and banking. P. gravis flies more rapidly with stiffer and more straight wings. The main feeding strategy of all three species is surface seizing and plunge diving with mostly only shallow dives to persue fish and cephalopods. However, the diving abilities of all three species are intermediate compared with Calonectris and the Sooty Shearwater A. grisea. Carneipes is known to dive easily to depths of 10-15 m and are observed reaching a maximum depth of 27 m (Oka 1994). Under water wings and feet are used for propulsion. As all shearwaters the three species are poor walkers and nest in burrows that are dug by themselves.

Osteology

The skulls of carneipes and creatopa are very similar which is consistent with their close relationship. The bill is more robust in comparison to gravis. The tubes are about one third of the culmen. The skull of gravis has a more slender bill with nostrils of about one quarter of the culmen length. The cranium of gravis is also more slender than that of the other species and has a more pronounced cerebellar prominence.

Great Shearwater Ardenna gravis, Flemish Cap, Atlantic Ocean
Culmen: 44.0 mm; total: 103.7 mm, unsexed adult.

Pink-footed Shearwater Ardenna c. creatopa, Robinson Crusoe Island, Chile
Culmen: 49.0 mm; total: 102.7 mm, adult male

Pink-footed Shearwater Ardenna c. creatopa Robinson Crusoe Island, Chile
Culmen: 39.3 mm; total: 95.1 mm, adult female

Flesh-footed Shearwater Ardenna c. carneipes. Oakura, NI, New Zealand
Culmen: 39.6 mm; total: 94.2 mm, adult, probably male