Petrel (White-chinned petrel) Procellaria aequinoctialis
Species: P. aequinoctialis
Binomial name: Procellaria aequinoctialis
Common names: White-chinned petrel, Cape hen
Procellaria aequinoctialis (White-chinned petrel) is a large shearwater a member of the Procellaria genus. It ranges around the Southern Ocean as far north as southern Australia, Peru and Namibia, and breeds colonially on scattered islands. They are South Georgia, Kerguelen Islands, Disappointment Island, Crozet Islands, Prince Edward Islands, Campbell Islands, Auckland Islands, Antipodes Islands, and the Falkland Islands. 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. During the non-breeding season, the petrels fly from the Antarctic pack ice to the subtropics.
The white-chinned petrel measures 51–58 cm in length, weighs 0.97–1.89 kg and spans 134–147 cm across the wings. 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 a black tip, and also black between the nostrils. It has black feet. When it flies, it mixes slow wing beats with glides. Although normally quiet, it will rattle or groan while at its colony. They have nasal passages that attach to the upper bill called naricorns. The nostrils on the petrel are on top of the upper bill. They produce a stomach oil made up of wax esters and triglycerides that is stored in the proventriculus. This can be sprayed out of their mouths as a defence against predators and as an energy rich food source for chicks and for the adults during their long flights. Finally, they also have a salt gland that is situated above the nasal passage and helps desalinate their bodies, due to the high amount of ocean water that they imbibe. It excretes a high saline solution from their nose.
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.
The survival of the White-chinned petrel has great significance as these birds are the last remnant of a unique ecosystem. They are one of the few petrel species that remain on the mainland of New Zealand and inhabit much of the same breeding range on the West Coast of the South Island as they did before humans arrived. Numerous species of burrowing petrels once bred in coastal and inland areas of both the North and South Islands. However, depredation by humans, changes to the habitat and predation by introduced mammals such as stoats, cats, dogs, pigs and rats have been responsible for the almost complete removal of petrels from the mainland. Fortunately, the large size and aggressive nature of Westland petrels allow them to more successfully defend themselves and their chicks against most predators, enabling them to survive where other petrel species have been lost. A late discovery was discovered as recently as 1945 when pupils of Barrytown School north of Greymouth found the distinctive blackish-brown bird with an ivory beak and black feet while doing a school project. (Wikipedia)
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