Cape hen, Shoemaker
The white-chinned petrel (Procellaria aequinoctialis ) also known as the Cape hen and shoemaker, is a large shearwater in the family Procellariidae. It ranges around the Southern Ocean as far north as southern Australia, Peru and Namibia, and breeds colonially on scattered islands. The white-chinned petrel was formerly considered to be conspecific with the spectacled petrel (Procellaria conspicillata ).
The white-chinned petrel measures 51–58 cm (20–23 in) in length and has a wingspan of 134–147 cm (53–58 in). Males are heavier and average 1,390 g (49 oz) whereas females weigh around 1,280 g (45 oz). Not only is it the largest Procellaria petrel but is also the largest species in its family outside of the giant petrels. This large petrel is sooty-black and has some white on its throat and chin, more so in the Indian Ocean sector than the Atlantic. Its primaries can have a silvery appearance underneath. Its bill may be horn or yellow with some black between the nostrils. It has black legs and feet. When it flies, it mixes slow wing beats with glides. Although normally quiet, it will rattle or groan while at its colony.
The white-chinned petrel utilises many islands during the breeding season. 2,000,000 pairs breed on South Georgia, Between 175,000 and 226,000 pairs are on the Kerguelen Islands, and 100,000 pairs on Disappointment Island. Some also breed on the Crozet Islands, Prince Edward Islands, Campbell Islands, Auckland Islands, Antipodes Islands, and the Falkland Islands. During the non-breeding season, the petrels fly from the Antarctic pack ice to the subtropics.
Their diet is composed mainly of krill followed by fish. White-chinned petrels feed by surface seizing and by undertaking shallow dives, and they will readily follow ships to collect fisheries discards, making them vulnerable to longline fisheries.
Both sexes help to build a nest, and will help incubate the egg. Upon hatching, both sexes again will assist in feeding and protecting the young.
A 2004 estimate placed the adult population at 7,000,000 with an occurrence range of 44,800,000 km2 (17,300,000 sq mi). Mortality of both adults and chicks due to longline fisheries has caused the IUCN to classify it as vulnerable. An overall decline in population is inferred by a drop in burrow occupancy rates of 28% at Bird Island, and an 86% reduction in population at Prydz Bay. Also, monitoring on Marion Island has shown of 14.5% reduction, and a 37% reduction on the Crozet Islands. Unintentional death at the hands of longline fisheries has proven to be a major contributor to the overall population decline. Nearly all of the bycatch from the Namibian hake are white-chinned petrels. 10% of the South African pelagic longline bycatch and 55% of the demersal. Also, the white-chinned petrel has suffered at the hands of invasive species such as the brown rat, Rattus novegicus, and the black rat, Rattus rattus.
Several of the breeding islands are protected areas. Ongoing studies and population monitoring are occurring at South Georgia, the Prince Edward Islands, Kerguelen Islands, and Crozet Islands. Finally, they are a part of ACAP Annex I, and CMS Appendix II.
To assist in reversing the decline in population it has been proposed to continue and extend monitoring studies, trying to eliminate most invasive species, promote adoption of best practice mitigation measures at all fisheries within the range via ACAP, FAO, CCAMLR.
