BRITAIN'S BIRDS AND THEIR NESTS. 55 



The nesting habits do not differ markedly from those of 

 the other Terns of this gi'oup. The nests are usually mere 

 ' scrapes,"" but sometimes with a lining of bent-grass, while 

 fairly bulky structures of this material are occasionally 

 found. The eggs are usually two in number in the British 

 Isles, but the commonest clutch in Mayo is said to be 

 three. They are about as large as those of the Black - 

 headed Gull, and are very variable in colour, creamy buff 

 to huffish stone-coloui', and usually boldly and handsomely 

 marked. The down-clad chicks are grayish buff above, 

 with dark mottlings, and gray and white colour below. 



THE BLACK TERN 



(Hydrochelidon nigra). 



As we have seen, five Terns of the typical group nest 

 in the British Isles ; but now we come to the sixth in- 

 digenous Tern, a member of the Marsh Tera group. The 

 Marsh Tems have proportionately shorter wings, veiy 

 slightly forked tails, and only half-webbed toes. Some of 

 them, including the present species, are characterised by the 

 prevalent dark hue of their breeding plumage. A centuiy 

 ago Black Terns nested in hundreds in the Norfolk Broads, 

 Lincoln Fens, and other suitable places ; but various causes 

 brought about their extermination, and the last recorded 

 British nest was in 1858. Now a few birds may be seen 

 each spring, but the species is chiefly known to us from 

 the migration of young birds past our coasts in autumn. 

 'Blue Dan-"' and 'Car Swallow' are among the local 

 names of the Black Tern. 



