Parasitic Jaeger | Stercorarius parasiticus

Voice

In this region it is almost always silent: to hear it you must go to the breeding grounds in the north. There it gives a nasal, cat-like ee-eh that suggests a mew, and over the territory a drawn-out wailing complaint. During a chase at sea a short chopping kek-kek occasionally escapes it, usually when two jaegers have picked the same tern. An observer in the southern hemisphere will hear no more than that.

Identification

A slender jaeger the size of a small gull, with narrow pointed wings and a fast, agile flight that suggests a falcon rather than a gull. The pale morph has a dark cap, yellowish cheeks, white underparts and usually a faint grey breast band; the dark morph is uniformly sooty brown, and in these waters that morph is well represented. Both show a pale flash at the base of the primaries, because a handful of feather shafts are white. Adults carry two pointed central tail feathers projecting five to eight centimetres beyond the tail. Young birds are warm brown and finely barred, with short blunt tail points, and are by far the hardest; the sexes look alike.

Confusion species

Pomarine Jaeger (Stercorarius pomarinus) is heavier built, with broader wings, a slower gull-like beat and, in the adult, central tail feathers broadened into a twisted spoon. Long-tailed Jaeger (S. longicaudus) is slimmer and colder grey above, lacks the breast band and carries very long thin tail streamers; it flies lightly and buoyantly like a tern and stays further offshore. Brown Skua (S. antarcticus) and South Polar Skua (S. maccormicki) are barrel-chested and heavy, uniformly brown with large white wing flashes, and do not hunt with a falcon's agility. Young birds of all the jaegers resemble each other; go on build, bill weight and the shape of the tail points, not on colour.

Habitat

Outside the breeding season — the only time it is here — it lives at sea: the band above the continental shelf, the mouths of bays and harbours, and the water just behind the surf where terns fish. It follows tern colonies, fishing boats and shoals of baitfish inshore, and appears in estuaries and over sandbanks where terns roost. On land it hardly occurs here, at most resting on a sandbar or a breakwater. It breeds on low Arctic tundra, far outside this region.

Range and movements

Breeds right around the North Pole, from Greenland, Iceland and Scotland to Siberia, Alaska and northern Canada, and leaves the north entirely after the breeding season. In the Australian summer it reaches the coastal waters of Australia and New Zealand; it is most numerous along the southeastern Australian coast, in the Tasman Sea and around both New Zealand main islands. Arrival falls in October and November and departure in March and April, with the occasional bird lingering through the Australian winter. On Norfolk it is a scarce visitor.

• Resident
• Non-breeding visitor
• dark = core range, pale = thinly spread

Where and when to look

Between November and March stand on a headland or a breakwater and look not for the jaeger but for the disturbance: a party of White-fronted or Greater Crested Terns suddenly scattering, with one dark bird below picking a single victim out of it. The chase often lasts half a minute and ends in a stoop in which the prize is caught in mid-air. On a pelagic trip it pays to look for the bird at the boat as soon as terns come in to the berley.

Conservation

Least Concern (LC): the world population is estimated at over three million birds. Regionally the picture is less easy — in the northeast Atlantic numbers have fallen sharply since the 1990s, because the terns and kittiwakes it lives off there are themselves breeding badly. For Australian and New Zealand waters there are no counts; what exists comes from the logs of pelagic trips and from seawatches along the coast.

Scientific name

Stercorarius parasiticus | (Linnaeus, 1758)

Linnaeus described the species in 1758 as Larus parasiticus, among the gulls; because it was later moved to another genus, author and year stand in parentheses. The genus Stercorarius was introduced by Brisson in 1760, after Latin stercus, 'dung': sailors believed the bird ate the droppings its victims released in flight, whereas in reality it was the disgorged fish. parasiticus means 'parasitic', after Greek parasitos, one who eats at another's table. Linnaeus gave as its origin the region within the Tropic of Cancer of Europe, America and Asia; the type locality was later restricted to the coast of Sweden.