Sooty Shearwater - Ecology and Status

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.