The adult in summer has the head, neck, and under parts dark greyish black, the rest of the plumage slate grey, except the vent and under tail coverts, which are white. Bill black. In winter the forehead, nape, chin, throat, and under parts are white. The young resemble the adults in winter, but the upper tail coverts are lighter and the back and wing coverts are greyish mottled with brown. Length 10 in.; wing 8·5 in.
THE WHITE-WINGED BLACK TERN
Hydrochelidon leucoptera (Schinz)
This species, which is nearly allied to the preceding, breeds in the marshes of Central and South-eastern Europe. It is a very scarce and irregular visitor to our eastern and south-eastern shores, especially in spring.
In habits it resembles the Black Tern, from which it may be distinguished in summer by its red bill, white tail and tail coverts, and whitish wing coverts. The young may be distinguished from those of H. nigra by their longer toes and much paler rump and tail. Length 9·5 in.; wing 8·25 in.
THE WHISKERED TERN
Hydrochelidon hybrida (Pallas)
This is a more southern species than its congeners, breeding in Spain, on the delta of the Rhone, and eastwards in Turkey, Greece, and South Russia. To our shores it is a very rare visitor, some half-a-dozen specimens only having been obtained.
In summer it is not unlike the Black Tern, but it may be recognised by the bill, which is stouter and red; the black of the head and nape is sharply contrasted with the grey of the back. A broad white stripe runs backwards from the base of the bill. Chin and throat grey, shading to black on the belly. In winter the forehead and under parts are white. Length 11·5 in.; wing 9·25 in.
THE GULL-BILLED TERN
Sterna anglica, Montagu
With this species we come to the true Terns or Sea-Swallows, the preceding species being known as Marsh Terns. The Gull-billed Tern is only a very scarce straggler to our shores, being a southern European species though occurring yearly as far north as Denmark.
In habits there is nothing to distinguish it from our commoner species.