Parasitic jaeger

Voice

Silent at sea; noisy only in the colony. There it gives a mewing, almost cat-like kee-aaw in display flight and a hard, nasal tuk-tuk as it dives at a walker or a fox. The recording offered here comes from a breeding site accordingly: a bird passing the Dutch coast will in practice make no sound at all.

Identification

Medium-sized and slim, with a fairly small head, a fine dark bill and a light, extremely agile flight. Adults occur in a pale and a dark morph with every intermediate: pale birds have a black cap, yellowish neck sides, white underparts and usually a faint greyish-brown breast band, while dark birds are uniformly sooty brown with a slightly paler head. The elongated central tail feathers of adults are straight, stiff and sharply pointed and project five to eight centimetres; by autumn they are often broken off. In every plumage there is a clear white primary flash above and below the wing, formed by four to six white shafts. Juveniles are warm brown to rufous, closely and finely barred, with a streaked head and a short but pointed tail projection.

Confusion species

Pomarine Jaeger is larger and heavier, with a barrel chest, slower and stiffer wingbeats, a heavier bicoloured bill and, in adults, twisted spoon-shaped streamers; its juveniles look colder greyish brown, have a plainer head and show a double white flash on the underwing instead of a single one. Long-tailed Jaeger is smaller and finer, with a short bill, grey rather than brown upperparts and almost no white in the hand. Great Skua is huge, uniformly brown, broad-winged and short-tailed. A jaeger chasing a Common or Sandwich Tern in over the dunes is, in the Netherlands, almost always this species.

Habitat

It breeds in loose colonies on coastal heath, tundra, islets and saltmarsh in northern Europe, usually within reach of tern and auk colonies whose catch it robs. Outside the breeding season it lives at sea, taking herring-family fish by chasing gulls and terns until they drop what they are carrying. On migration it follows the coastline and the movement of terns, and so comes closer inshore than the other jaegers.

Range and movements

It breeds from Iceland and Scotland through Norway and Sweden to northern Russia; the Orkney and Shetland colonies have more than halved within a few decades. The Netherlands has no breeding birds but a clear passage: from late July to mid-October several thousand pass along the coast each year, by far the most of them on strong westerlies. In Spain it is a regular migrant off the Cantabrian and Galician coasts and through the Strait of Gibraltar, in smaller numbers along the Mediterranean too.

• Breeding (summer)
• Winter
• Passage
• dark = core range, pale = thinly spread

Where and when to look

Pick a seawatching point — Camperduin, Westkapelle, the Brouwersdam or the head of a pier — on a north-westerly of force 5 to 7 in August or September, and watch the first three hours after sunrise. Above all, watch the terns: where a party of Common or Sandwich Terns suddenly turns edgy, there is nearly always a Parasitic Jaeger in it. With offshore wind and a flat sea the odds are poor; here the weather matters more than the date.

Conservation status

Least Concern globally, but the European breeding population is falling fast: down by well over half on the Scottish isles since the 1990s. Food shortage following the collapse of the sandeel stock, and predation by the much larger Great Skua, are the main causes. Norway and Iceland look somewhat better, but declines are reported there too, and passage along our coast follows that trend with a lag.