FORK-TAILED PETREL.
A year after this species was first described by Vieillot, under the name of Procellaria leucorhoa, it was discovered at St. Kilda by Bullock. This was early in the present century, but the islands, known collectively by that name, still continue to be its most famous breeding place in our area, or even in Europe. Three years after its discovery, it was rechristened P. leachi by the French naturalist Temminck, a name which has found favour with many writers. The Fork-tailed Petrel is known to breed on North Rona, and at some other spots in the Outer Hebrides, as well as on the Blaskets off the coast of Kerry. There can be little doubt that many other breeding stations of this Petrel remain to be discovered. This species, readily distinguished from the Stormy Petrel by its larger size and deeply-forked tail, is rarely seen near the land unless during the breeding season, or when driven thence by boisterous weather. I have known it to be caught in the flight-nets on the mud-banks of the Wash; whilst it is of tolerably frequent occurrence elsewhere off our eastern and southern coasts. In its habits generally it very closely resembles its better known ally, the Stormy Petrel. During the non-breeding season it wanders vast distances from land, sleeping and resting on the sea when tired, following ships for miles, fluttering along close to the ocean, now down into the trough of the wave, anon skimming over the crest to half-fly, half-run, with patting feet, down the smooth surface of the next. Except during the breeding season this Petrel is not very gregarious; it may often be seen in parties of perhaps half-a-dozen, scattered over a considerable surface of water. The exact nature of the food of this species is apparently unknown. It is said, in a vague and general way, to feed on crustaceans and small molluscs, and the scraps of refuse cast from passing vessels, but birds which I have dissected contained similar substances to those found in the Fulmar—a nearly clear oil, mingled with the jaws of cuttlefish, and scraps of sorrel.
The Fork-tailed Petrel resorts to its breeding stations to nest in June. Although gregarious during this period, its colonies are never so large as those of the Fulmar. Most probably the bird pairs for life, and returns season by season to certain spots to rear its young. The largest colony of this Petrel known to me is at St. Kilda. Here its principal colony is located on the island of Soay, but there is another and smaller one on Doon, and doubtless others on Borreay. At the colony on Doon, the ground was full of long, winding burrows, probably disused nesting holes of Puffins and Shearwaters, and in these the Fork-tailed Petrels had made their nests—in some cases one earth accommodating several pairs of birds. Usually the selected burrows are in the loamy soil near the summit of the cliffs; but, in some cases, the birds will select a hole, or crevice, in ruined masonry, or in rocks. At the end of the burrow, or crevice, a scanty nest of dry grass is formed, but in some cases no provision whatever is made. Here the female deposits a single egg, white, with a zone of dust-like brown specks round the larger end. These eggs are remarkably fragile, and very chalky in texture. The Fork-tailed Petrel is a close sitter, remaining brooding over its egg until dragged out. Many nests may be found within an area of a few yards. This Petrel is not seen abroad much at its breeding places during daylight; all day long the little birds skulk in their burrows, but with the approach of night, they begin to sally forth from their retreats and nests, and their fluttering forms may be seen flitting to and fro in the deepening gloom, backwards and forwards, to and from the sea. The Fork-tailed Petrel is not a very noisy bird. Those that I dragged from their nests uttered a few squeaking notes; but at night the species becomes more garrulous. But three breeding stations of this Petrel are known—one in the North Pacific, another in the Bay of Fundy, and the third within the British area. Its migrations are limited.