Shearwater (Sooty) Ardenna grisea

Kingdom: Animalia
Phylum: Chordata
Class: Aves
Subclass: Neornithes
Infraclass: Neognathae
Superorder: Neoaves
Order: Procellariiformes
Family: Procellariidae
Genus: Ardenna
Species: A. grisea
Binomial name: Ardenna grisea
Synonym: Puffinus griseus, Ardenna grisea grisea
Common name: Sooty shearwater, Muttonbird, titi

Ardenna grisea is an abundant shearwater, breeding on islands off New Zealand, Australia and Chile, and the Falkland Islands (Malvinas). In Australia there are colonies on 17 islands (all of less than 1,000 pairs), southern Chile (many colonies, some up to 200,000 pairs and up to 4 million birds on Isla Guafo; Reyes-Arriagada et al. 2007) and the Falklands (10,000-20,000 pairs) and more than 80 colonies in New Zealand (totalling c.5 million pairs) (Marchant and Higgins 1990). In 1970-71, the Snares Islands colonies were estimated to support 2,750,000 breeding pairs (del Hoyo et al. 1992; Heather and Robertson 1997). The total world population is thought to be over 20 million birds (Heather and Robertson 1997).
Ardenna grisea is a medium-large, chocolate-coloured, shearwater with a length of 40–51 cm and a wingspan of 94–110 cm. There is a silvery strip along the centre of the underwing. It has the typical "shearing" flight of the genus, dipping from side to side on stiff wings with few wing beats, the wingtips almost touching the water. Its flight is powerful and direct, with wings held stiff and straight, giving the impression of a very small albatross. it shows as dark chocolate-brown a silvery strip along the centre of the underwing.
The sooty shearwater feeds on fish, crustacea and cephalopods. They can dive up to 68 m deep for food, but more commonly take surface food, in particular often following whales to catch fish disturbed by them. They will also follow fishing boats to take fish scraps thrown overboard.

Ardenna grisea start breeding in October. They nest on islands and headlands and breed in huge colonies. Burrows are dug for breeding under tussock grass and low scrub and the female lays one white egg. These shearwaters nest in burrows lined with plant material, which are visited only at night to avoid predation by large gulls. The breeding grounds are usually noisy due to the birds cooing and croaking. They incubate their young for about 54 days. Once the chick hatches, the parents raise their chick for 86 to 109 days. Short (1-3 days) and long (5-15 days) provisioning trips are made by parents. After leaving the breeding grounds birds typically do not return to their natal colonies until the age of four.

Ardenna grisea are spectacular long-distance migrants covering distances in excess of 14,000 km. They following a circular route, travelling north up the western side of the Pacific and Atlantic Oceans at the end of the nesting season in March-May, reaching subarctic waters in June–July where they cross from west to east, then returning south down the eastern side of the oceans in September–October, reaching to the breeding colonies in November. They do not migrate as a flock, but rather as single individuals, associating only opportunistically.  
In the Atlantic Ocean, they cover distances in excess of 14,000 km from their breeding colony on the Falkland Islands (52°S 60°W) north to 60 to 70°N in the North Atlantic Ocean off north Norway; distances covered in the Pacific are similar or larger; although the Pacific Ocean colonies are not quite so far south, at 35 to 50°S off New Zealand, and moving north to the Aleutian Islands, the longitudinal width of the ocean makes longer migrations necessary. Recent tagging experiments have shown that birds breeding in New Zealand may travel 74,000 km in a year, reaching Japan, Alaska and California, averaging more than 500 km per day.

In New Zealand, about 250,000 mutton birds are harvested for food each year by the native Māori. Young birds when they are just about to fledge are collected from the burrows, plucked, and often preserved in salt.

The story of muttonbirding in New Zealand.

Sooty shearwater by Sabine's Sunbird.jpg   

A.griseus by Marlin Harms.jpg

Thanks to Wikipedia for text and information