The mottled petrel (Pterodroma inexpectata) is a medium-sized and distinctive petrel species, most easily identified by the grey patch on its lower breast and belly, which contrasts with the otherwise white underparts (2)(3)(4)(5). The upperparts of the mottled petrel are grey, with a darker ‘M’ shape across the back, rump and wings (2)(3)(4)(5). The face is white, mottled with grey and with a dark patch behind the eye (3)(4)(5). The underside of the wing is white, with a broad black band running diagonally from the bend of the wing towards the body (3)(4)(5), and the tip and trailing edge of the underwing are dark (3).
The mottled petrel has a small black bill and dark eyes. Its legs are pink, and the webbed feet are black on the outer edges (3)(4)(5). Juvenile mottled petrels are identified by the more scaly appearance of the upperparts (2).
The main call of the mottled petrel, given either in the air or from the ground, is a far-carrying ‘ti-ti-ti’. However, it has quite a diverse repertoire and also produces various growling and crooning noises, as well as a call described as ‘gor-wik’(3)(6).
The mottled petrel feeds mainly on squid, fish and some crustaceans, taking prey from or plunging just below the surface of the sea. It sometimes feeds in association with the sooty shearwater, Puffinus griseus(2)(3). The flight of the mottled petrel is typical of gadfly petrels, consisting of fast, high arcs and sustained glides (5).
Adult mottled petrels return to the breeding colonies in October and November, with most egg-laying occurring over a limited period of about a week in December (3)(4)(6). The nesting burrow may be built in a variety of locations, but is usually in contact with rock. The burrow extends for up to one metre and ends in an enlarged chamber, lined with grass. Breeding pairs usually stay together and use the same burrow from year to year (3)(6).
This species lays a single egg, which is incubated by both the male and female for around 50 days. Each incubation shift lasts between 12 and 14 days, giving the non-incubating adult time to travel huge distances to feeding grounds in the Antarctic. The newly hatched mottled petrel is covered in grey down and is brooded by the adults for one to two days (2)(3)(6), after which both adults forage and bring food back to the chick. The adults only return to the colony at night, possibly to avoid predation by the brown skua (Catharacta lonnbergi) (3)(6). The young mottled petrel fledges at around 90 to 105 days old (2)(3)(6) and departs from the colony by early June (6).
The mottled petrel breeds only in New Zealand. It formerly bred throughout the North and South Islands, as well as possibly on the islands of Chatham, Bounty, Antipodes and Auckland. However, it is now found only on and around Fiordland, the Solander Islands, islands off Stewart Island and in the Foveaux Strait, and on islands in The Snares (2)(3)(4)(5)(7). During the breeding season, the mottled petrel forages widely at sea, occurring as far south as the pack ice of Antarctica (2)(3)(4)(7).
After breeding, the mottled petrel migrates north to the North Pacific, as far as the Bering Sea (2)(3)(4)(5)(7), and is rarely seen within 50 kilometres of land (3). There is also at least one record of this species from the North Atlantic, off the coast of North Carolina in the USA (2).
A highly pelagic species, the mottled petrel spends most of its life far out at sea, only coming to land to breed (2)(3)(7). Breeding takes place in dense colonies on offshore islands and rock stacks, with the nest being built in a burrow, rock crevice or cave, in rocky ground or tussock grassland (2)(3)(6)(7).
This poorly known petrel breeds only on a few relatively small islands around New Zealand. On many of these, the mottled petrel is believed to be declining due to predation by introduced species such as the black rat (Rattus rattus) and the weka (Gallirallus australis) (2)(7). It may also be affected by the harvest of sooty shearwater chicks (Puffinus griseus) on some islands, which could potentially result in the trampling of nesting burrows and the accidental taking of petrel chicks (7).
The mottled petrel is likely to have been wiped out on most of mainland New Zealand by harvesting for human consumption and predation by introduced mammals (2)(3). It may also have been affected by forest clearance (2).
There are no known conservation measures currently in place for the mottled petrel (7). This species would benefit from population monitoring (7), as well as the elimination of introduced predators at its breeding sites and the prevention of further introductions (2)(7). The impact of the sooty shearwater chick harvest on the mottled petrel also needs to be assessed (7).
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Diverse group of animals with jointed limbs and a hard chitinous exoskeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.
The act of incubating eggs; that is, keeping them warm so that development is possible.
Sea ice that floats on the surface of the water. Often formed from large pieces of ice that consolidate into a single ice mass, pack ice typically moves with currents, tides and wind.
In birds, applied to sea birds that come to land only to breed, and that spend the major part of their lives out at sea.
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