A member of a group of small seabirds know as prions, the thin-billed prion (Pachyptila belcheri), or slender-billed prion, is named for its very narrow bill, with which it takes marine crustaceans. Like most other prions, it has pearl-grey upperparts and white underparts. It also has a conspicuous, narrow, black ‘W’ mark on the wings that is most visible when it is in flight (3). The tail has a narrow black band at the tip, bordered by white outer tail feathers, and a long blackish bar runs up the centre of the underside (2). The forehead and crown of the thin-billed prion are darkish grey, there is a grey collar around the neck, and the legs and feet are bluish, tinged with pink on the webs (3). The thin-billed prion may also be identified by its facial markings, comprising a black line behind each eye and a longer white eye-stripe (2).
A gregarious species, the thin-billed prion is often found in large groups in areas where food is abundant. Like other prions, it is also often found in the presence of cetaceans which drive prey towards the surface, hence these species’ alternative name of ‘whalebirds’. The thin-billed prion mainly feeds on planktoniccrustaceans, but occasionally also eats some fish and squid. It hunts mainly by seizing its prey near the water surface, but will also plunge into the water and catch its prey after a very short pursuit underwater (2)(4).
Breeding thin-billed prions normally arrive back at the breeding colonies in late August, around three weeks before egg laying begins. A single egg is laid in a burrow in soil or sand, under rocks or below dense vegetation. The egg is incubated for 46 or 47 days, with the chick hatching in late December or early January. Young thin-billed prions fledge after 49 days (3).
The thin-billed prion breeds in two distinct areas: on the Crozet and Kerguelen Islands in the southern Indian Ocean, and on the Falkland Islands in the southwest Atlantic and Noir Island in the southeast Pacific (3).
Outside of the breeding season, it ranges over much of the Southern Ocean, including the coasts of South Africa, Australia and South America, as far north as Uruguay and southern Peru (4). During this period, thin-billed prions breeding in the southern Indian Ocean typically travel towards Australia and New Zealand, while breeding birds from the Falklands and Noir Island tend to move west into the Pacific Ocean (3).
A marine species, the thin-billed prion is usually found over deep waters far out at sea, although it will also feed in shallow offshore waters during the breeding season (4). It breeds in coastal areas, with soft or stony soil and low vegetation (2).
With a stable global population estimated at 7 million individuals in 2004 (3), the thin-billed prion is a common species that is not currently threatened with extinction (4). No major threats to the survival of this species have yet been identified. On the Falkland Islands, the thin-billed prion is perhaps the most abundant seabird species (5).
In the absence of any major threats to the thin-billed prion, it has not been the target of any known conservation measures (4). However, it is likely that this species has benefited from a number of habitat restoration measures that have been undertaken within its range. On the Falkland Islands, for instance, tussock grass has been replanted where grazing by introduced sheep has degraded natural vegetation, while regular rubbish clean-ups are conducted on beaches. Eradication programmes have also been conducted to remove invasive plants and introduced predators, such as rats, which may predate ground-nesting seabirds. In addition, strict regulations are in place to prevent man-made fires from destroying habitat (6).
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A group comprising all whales, dolphins and porpoises.
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.
To keep eggs warm so that development is possible.
Aquatic organisms, usually tiny, that drift passively with water movements; may be phytoplankton (plants), zooplankton (animals), or other organisms such as bacteria.
Catry, P., Campos, A., Seguarado, P., Silva, M. and Strange, I. (2003) Population census and nesting habitat selection of thin-billed prion Pachyptila belcheri on New Island, Falkland Islands. Polar Biology, 26: 202-207.
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