Birds – Parasitic Jaeger

(Stercorarius parasiticus)


Length-17.20 inches.

Male and Female—Light stage: Top of head and cheeks brown, nearly black; back, wings, and tail slaty brown, which be-comes reddish brown on sides of breast and flanks. Sides of head, back of neck, and sometimes entire neck and throat yellowish. Under parts white. Wings moderately long, strong and pointed. Middle feathers of tail longest. Black tip of upper half of slate-colored bill is swollen and rounded over end of lower mandible like a hawk’s. Feet black. Dark stage : Plumage dark slaty brown, darker on top of head, very slightly lighter on under parts. Immature specimens, which seem to be most abundant off our coasts, show sooty slate plumage; bordered, tipped, or barred with bully, rufous, or brownish black, giving the bird a mottled appearance. Plumage extremely variable with age and season.

Range—Nests in Barren Grounds, Greenland, and other high northern districts; migrates southward along the Atlantic and Pacific coasts and through the Great Lakes, wintering from New York, California, and the Middle States to Brazil.

Season—October to June. Winter visitor.

This dusky pirate, strong of wing and marvelously skilful and alert in its flight, uses its superior powers chiefly to harass and prey upon smaller birds. Lashing the air with its long tail, and with wide wing stretchings and powerful strokes, the jaeger comes bearing down on a kittiwake gull that holds- a dripping fish ready for a contemplated dinner. To dart away from its tormentor, that darts, too, even more suddenly; to outrace the jaeger, although freighted with the fish, are tried resorts that the little gull must finally despair of when the inevitable moment arrives that the coveted fish has to be dropped for the pirate to snatch up and bear away in triumph.

Other gulls than the kittiwake suffer from this ocean prowler; their young and eggs are eaten, their food is taken out of their very mouths. As they live so largely on the results of other birds’ efforts, the jaegers deserve to be branded as parasites, which all the group are. Indeed, these birds that the English call skuas, differ very little, if any, in habits. While all spend the summer far north, the parasitic jaeger has really less claim to the title of Arctic jaeger than either the pomarine or the long-tailed species, which go within the Arctic Circle to nest. On an open moor or tundra, in a slight depression of the ground, a rude nest is scantily lined with grass, moss, or leaves. Sometimes this nest is near the margin of the sea or lake, sometimes on an ocean island and laid among the rocks. It contains from two to four—usually two—light olive-brown eggs that are frequently tinged with greenish and scrawled over with chocolate markings most plentiful at the larger end, where they may run together and form a blotch.

By the end of September the jaegers begin their southerly migration, reaching Long Island in October, regularly, and quite as regularly leaving early in June. During the winter they play the role of sea scavengers when they are not robbing the gulls, that will actually disgorge a meal already safely stowed away rather than submit to the harassing, petty tortures of these pirates. Jaegers constantly pick up carrion and other rubbish cast up by the sea or thrown overboard from a passing ship, for nothing in the line of food, however putrid it may be, seems to miss the mark of their rapacious appetites, as their Latin name, stercorarius, a scavenger, indicates. On land they always seek choicer food, garnered by their own effort—berries, insects, eggs, little birds, and mammals.

The best trait the jaegers have is their uncommon courage. Nothing that attacks their home or young is too large or fierce for them to dash at fearlessly ; and by persistent teasing and harassing, for the want of formidable weapons of defense, they will eventually get the better of their antagonist, though it be a sea eagle.

The Pomarine Jaeger—a contraction of pomatorhine, meaning flap-nosed—(Stercorarius pomarinus) may be distinguished from the parasitic jaeger by its larger size, twenty-two inches; by the rounded ends of its central tail feathers, which project about three inches beyond the others; and finally by its darker, almost black, upper parts, although the plumage during the dark and the light phases of these birds is so nearly the same that when seen on the wing it is impossible to tell one species from another. Professor Newton, of Cambridge University, has noted that the long, central tail feathers of the pomarine jaeger have their shafts twisted toward the tip, so that in flight the lower surfaces of their webs are pressed together vertically, giving the bird the appearance of having a disk attached to its tail. This species is also called the pomarine hawk-gull.

It is not known whether the Long-tailed Jaeger, or Buffon’s Skua, as they call it in England (Stercorarius longicaudus), undergoes the remarkable changes of plumage that its relatives indulge in or not, for its range is more northerly than that of any of the jaegers, and when it migrates south of the Arctic Circle, to our coasts, it is wearing feathers most confusingly like those of the parasitic jaeger in its light phase. Indeed, the young of these two species cannot be distinguished except by measuring their bills, when it is found that the long-tailed jaeger has the shorter bill.

The distinguishing mark of the adults of this species is the length of the central tail feathers, narrow and pointed, that project about seven inches beyond the others; but immature specimens lack even this mark. The description of the habits of the parasitic jaeger applies equally well to all of the three freebooters mentioned.