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Slender-billed Prion | Pachyptila belcheri
Dunbekprion | Pato petrel picofino
The Slender-billed Prion is the palest and finest built of the six whalebirds, and the only one that does not breed in this map window: it comes in winter from the Falklands, Kerguelen and the Crozets to the sea below Australia and New Zealand. At 9.5 to 12.5 mm its bill is the narrowest in the genus — less than half the width of a Broad-billed Prion's — and its face is strikingly white.
Voice
Within this map window it is mute: it does not breed here and prions are silent at sea. At the colonies on the Falklands and Kerguelen it is noisy at night, with a hard rattling chatter from the burrows and a softer, dove-like crooning between; pairs call to one another in the burrow entrance with short purring notes. Anything heard here is at most the faint squeaking of an exhausted, beach-wrecked bird.
No freely licensed recording has been found for this species yet; what to listen for is described below.
Identification
About 26 cm long and 145 g, but slimmer and longer-winged in impression than the other prions of that size. Blue-grey above with the black M across the wings, white below. The face is the feature: paler than in any other prion, with a broad, sharply drawn white eyebrow over a dark eye-stripe, which gives the head a boldly white-and-dark striped look. The tail is wedge-shaped grey with a narrow black tip, far less conspicuous than the broad tip of Fairy and Fulmar Prions. The bill is pale blue-grey, straight and exceptionally narrow.
Confusion species
Antarctic Prion (Pachyptila desolata) is the case that arises most often, since the two occur here in the same winters and often in the same flock: desolata has a wider bill (11–15.5 against 9.5–12.5 mm) and a clearly darker, greyer face with a less sharply cut eyebrow. Salvin's Prion (Pachyptila salvini, 13.5–17.5 mm) and Broad-billed Prion (Pachyptila vittata, 18.7–24.3 mm) have a far heavier, darker bill and a darker head; in Broad-billed the grey runs down onto the upper breast. Fairy Prion (Pachyptila turtur) and Fulmar Prion (Pachyptila crassirostris) are smaller and more compact, with a plainer grey head lacking that sharp eyebrow and a much broader black tail tip. At sea the pale face remains the first thing to catch the eye, but without a good head photograph it is wise to leave the bird at 'prion sp.'.
Habitat
Open subantarctic and cool temperate ocean, outside the breeding season nearly always well offshore; it comes near land only when the wind drives it there. It feeds at the surface on small crustaceans — chiefly amphipods and krill — and on small squid, hydroplaning with wings held open and the bill half in the water. On the breeding grounds, outside this map window, it digs burrows in soft peat under tussock and Azorella cushions.
Where the bird is most often found, arranged by main group and formation.
Range and movements
It does not breed in the New Zealand or Australian region: the colonies lie on the Falkland Islands (over a million pairs), on Kerguelen (700,000 to a million pairs), on Isla Noir off southern Chile and on the Crozets. In this map window it is a winter visitor to the southern sea and the shelf edge, commonest off the south coast of Australia and Tasmania. In New Zealand it occurs in small numbers and is found chiefly late in winter, wrecked on beaches on the west coast of the North Island.
- Resident
- dark = core range, pale = thinly spread
Where and when to look
Look for it in July and August: pelagics out of Port Fairy, Portland or Eaglehawk Neck give the best chance, and after a south-westerly gale a walk along a south coast beach, or a North Island west coast beach, is worth the effort. Photograph the head of every prion in strict profile; the contrast between the white eyebrow and the dark eye-stripe is stronger in this species than in any other prion, and together with the narrow bill it is the only thing that holds up on a photograph taken at sea.
Conservation
Least Concern (LC): the world population is over two million pairs, making it one of the most numerous seabirds of the southern ocean. The main concern is feral cats on Kerguelen, which kill large numbers of adults at the great colonies there each year. Beyond that count storm mortality — in bad years hundreds to thousands wash up on Australian and New Zealand beaches — and the exposure of a plankton feeder to changes in sea temperature.
Scientific name
Pachyptila belcheri | (Mathews, 1912)
Mathews described the species in 1912 as Heteroprion belcheri; because the genus has since changed, author and year carry parentheses. The epithet honours Charles Belcher, an Australian judge and amateur ornithologist who found the first specimens on a beach near Geelong in Victoria — and Geelong is accordingly the type locality, which is remarkable for a bird that breeds nowhere in Australia. The genus Pachyptila was introduced by Illiger in 1811, from Greek pakhus 'thick' and ptilon 'feather'. The Maori name is korotangi.