Highway Robbery.
The osprey rose with its prey when the eagle swooped, but by swerving, the osprey momentarily escaped. The eagle is shewn stopping himself against the wind, to swoop again with fiendish cries until the osprey drops his prey in terror.
Other piratical plunderers are the skuas and some other members of the gull family. With the former the practice is more habitual, or, rather, it is pursued more to the exclusion of other habits of feeding. In the more northern parts of the British Isles—especially in the Orkneys and Shetlands—the lesser or arctic skua may be seen all day long during the breeding season, taking toll of the various sea-fowl, as they fly with fish to feed their young. One might think that when once the fish had been swallowed there would be an end of the annoyance, and that the rightful owner must, by the very nature of things, now be safe. Such, however, is by no means the case. Most birds have no difficulty in bringing up again what they have swallowed down.[1]
The skua, when it swoops upon a gull, does so with the deliberate intention of forcing it to disgorge the fish it has swallowed, which it then, like the eagle, catches in the air before it has touched the sea. Should it not succeed in doing this, the fisherman asserts that it will not touch it, but invariably leaves it lying on the water, or on the land, should it chance to fall there. I have myself seen skuas act in this manner, but am not so satisfied that it is their invariable practice. Terns, should there happen to be a colony in the neighbourhood, are particularly persecuted by these skuas, insomuch that the gulls derive a distinct benefit from their presence. Puffins and guillemots are also pursued, and so ingrained is the habit of piracy that the skuas will sometimes, as it were, play at it, swooping at and chasing one another in the same manner and with the same wild cries as when they practise the art in earnest. Of course, under these circumstances neither bird disgorges to the other, and it is easy to see that neither expects the other to do so.
Though gulls uniformly suffer at the hands of the skuas, they can be pirates too amongst each other, and in harbour or where fishing-smacks are anchored nothing is commoner than to see a bird that has seized on some offal of fish thrown overboard mobbed by a host of others, till the morsel reappears again de profundis.
Only one British gull, however, as far as I know, has taken up piracy as a profession, and that is the black-headed one. It is difficult in works of natural history to find any reference to this interesting fact, but it seems to be alluded to in one of the common or local names of this species, viz. the peewit-gull. For here the parasitic relation is between a sea-bird and a land-bird—the peewit, namely—which to me makes it still more interesting. At certain times of the year, and in certain parts of the country, almost every field or piece of land near the sea-shore in which peewits are feeding is sure to have a few of these gulls scattered about it. They stand, apparently, doing nothing, but are really keenly on the look-out, and as soon as a peewit has found anything, come sweeping down upon it. In the chase which ensues the pirate is not always successful, but very generally the peewit drops his booty, and the gull either catches it in the air or picks it up off the ground.
In all the above kinds of robberies the young of the piratical species are fed more or less frequently with the food carried off by it from the various victims. This, however, is only incidental to the main habit, so that there is little in these bird doings to remind us of those horrid relations between insect and insect, with some examples of which this chapter opened, wherein one species is wholly sacrificed for the sake of the young of another. There is, however, a nearer approach to this—since though the effects are less tragic, the governing cause is the same—in that instinct which impels some few birds to lay their eggs in the nests of other species. Here, as the services of the foster parent are required, it does not itself suffer, but its own young perish to make place for the stranger. One most familiar example of this more advanced and complicated kind of parasitism is, of course, the cuckoo, but as the habits of this bird have been treated of in so many books, I need say nothing of them here.