WatchList Species Account for Sooty Shearwater |
Qualifies for the list as a Declining Yellow List Species
|Photo: Glen Tepke
The Sooty Shearwater is a seabird with populations estimated in the tens of millions, often visible from shore along the Pacific Coast during migration. A spectacular long-distance migrant, it covers great distances, following a circular route, up the western side of the Pacific and Atlantic at the end of the nesting season to subarctic waters in June and July, then returning to the breeding colonies in the south down the eastern side of the oceans in September and October, arriving at its destination in November. Tagging experiments indicate that some individuals may cover up to 40,000 miles in a single year.
Its large breeding colonies are on small islands in the southern oceans, principally around New Zealand (which has approximately half the population), the Falkland Islands, and Tierra del Fuego, but also on islands off Australia. The bird nests in burrows, where it lays a single egg. As is the case with many seabirds, it visits its nest only at night.
The Sooty Shearwater feeds on fish and squid and can dive for food to a depth up to 223 feet for food, though they more commonly take food from the surface, often following whales to catch fish disturbed by them. It also follows fishing vessels to feed on fish scraps thrown overboard.
Mortality factors include harvesting young birds or 'mutton birding,' particularly by Maoris following traditional practices in New Zealand, which currently accounts for around a quarter of a million of birds annually, but is not thought to be a major reason for the scale of the decline. Formerly populations are no longer prey to pelagic drift-nets, which drowned up to 350,000 birds annually.
There is some indication that the popultion may be diminishing. From 1976 to 1996, the number of migrating shearwaters in the California Current is estimated to have fallen by 90%. This period saw an increase in ocean temperature and an accompanying fall in productivity in the California Current, with decreases in the numbers of other seabirds as well, though less pronounced than that seen among Sooty Shearwaters. Though the assumption exists that these decreases are the result of human-induced climate change, bird’s numbers may be influenced by naturally occurring variations. IUCN now lists the bird as “near threatened,” while New Zealand lists it as being in “gradual decline.”