The Sooty Shearwater (Puffinus griseus) is a medium-large shearwater in the seabird family Procellariidae. In New Zealand it is also known by its Māori name tītī and as "muttonbird", like its relatives the Wedge-tailed Shearwater (P. pacificus) and the Australian Short-tailed Shearwater (P. tenuirostris).
It appears to be particularly closely related to the Great ("P." gravis) and Short-tailed Shearwaters, all blunt-tailed, black-billed species, but its precise relationships are obscure. In any case, these three species are among the larger species of shearwater which might belong into a separate genus Ardenna.
Sooty Shearwaters are 40–51 cm in length with a 94–110 cm wingspan. 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. This shearwater is identifiable by its dark plumage, which is responsible for its name. In poor viewing conditions, it looks all black, but in good light, it shows as dark chocolate-brown a silvery strip along the center of the underwing.
Usually loud, Sooty Shearwaters coo and croak while on the breeding grounds.
In the Atlantic, it is the only such bird, whereas in the Pacific part of its range, other all-dark large shearwaters are found. The Short-tailed Shearwater in particular is almost impossible to tell apart from the present species at a distance.
Distribution and movements
Sooty Shearwaters breed on small islands in the south Pacific and south Atlantic Oceans, mainly around New Zealand, the Falkland Islands, Tierra del Fuego and also in the Auckland Islands and Phillip Island off Norfolk Island. They start breeding in October, and incubate their young for about 54 days. Once the chick hatches, the parents raise their chicks for 86 to 109 days.
They are spectacular long-distance migrants, 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 sub Arctic 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 June 1906 for example, two were shot near Guadalupe Island off Baja California (Mexico), several weeks before the bulk of the population would pass by. Likewise, the identity of numerous large dark shearwaters observed in October 2004 off Kwajalein in the Marshall Islands remains enigmatic; they might have been either Sooty or Short-tailed Shearwaters, but neither species is generally held to pass through this region at that time.
In the Atlantic Ocean, they cover distances in excess of 14,000 km (8,700 mi) 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 Great Britain, they move south in late August and September; with strong north and north-west winds, they may occasionally become 'trapped' in the shallow, largely enclosed North Sea, and heavy passages may be seen flying back north up the British east coast as they re-trace their steps back to the Atlantic over northern Scotland.
Ecology and status
The Sooty Shearwater feeds on fish and squid. 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.
They breed in huge colonies 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.
In New Zealand, about 250,000 mutton birds are harvested for oils, food and fats each year by the native Māori. Young birds just about to fledge are collected from the burrows, plucked, and often preserved in salt.
Its numbers have been declining in recent decades, and it is presently classified as Near Threatened by the IUCN. In 2009, the harvest reported record-low catches, on average a trapping cage would yield nearly 500 birds; in 2009 the number was estimated to be closer to 40 per cage.
Numbers of breeding pairs are currently (2011) estimated at 22 million pairs. The above harvest information cannot in any way be considered accurate, as the methods used by the Rakiura Maori to harvest chicks do not include any form of trapping cage. The methods used are the nanao which consists of tracing the burrows of the birds, digging into the tunnel and removing the chick; this occurs in the early stages of the season (1 April) and the rama (torching), which is night catching of the young birds which exit their burrows on dark rainy nights to commence fledging. The season ends on 31 May, by which time all of the birds have left on their migration. Whilst 2009 was indeed a kiaka or bad season, these occur on average every seven years, and the following two seasons, 2010 and 2011, were good years with plenty of birds.
Muttonbirding also has less impact on the wider population of titi than one may suspect, as the titi bird always returns to the same nesting site, so it is only the bird populations of the "Muttonbird Islands" themselves (a small percentage of the total breeding stock) which are impacted in any way.
Inspiration for Hitchcock's The Birds
On August 18, 1961, the Santa Cruz Sentinel reported thousands of crazed sooty shearwaters were sighted on the shores of North Monterey Bay in California, regurgitating anchovies, flying into objects, and dying on the streets. The incident sparked the interest of local resident Alfred Hitchcock, along with a story about spooky bird behavior by British writer Daphne du Maurier, helping to inspire Hitchcock's 1963 thriller The Birds, a cautionary tale of nature revolting against man. The film is now ranked among the American Film Institute's Top 10 thrillers of the last century.
Scientists looking at the stomach contents of turtles and seabirds gathered in 1961 Monterey Bay ship surveys have found toxin-making algae were present in 79% of the plankton the creatures ate. "I am pretty convinced that the birds were poisoned," says ocean environmentalist Sibel Bargu of Louisiana State University. "All the symptoms were extremely similar to later bird poisoning events in the same area."
Plankton expert Raphael Kudela of USC points to leaky septic tanks installed amid a housing boom around Monterey Bay in the early 1960s as the ultimate culprit that may have fed the toxic algae "It is to some extent a natural phenomenon, and the best thing we can do is monitor for the presence of toxins, and treat impacted wildlife."
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