4 ALLEN S NATURALISTS LIBRARY. 



mantle ; the head and nape blackish, the forehead whiter ; 

 round the hind neck a broad collar of white ; sides of face and 

 under surface of body pure white, excepting for a patch of 

 ashy-brown on each side of the upper breast. 



Adult Male. General colour above slate-grey, a little paler on 

 the wing-coverts, the small coverts round the carpal bend of 

 the wing being white ; the bastard-wing, primary-coverts, and 

 quills dark slaty-brown, externally frosted with light ashy-grey, 

 and paler grey on the inner web, the shafts of the primaries 

 white ; the upper tail-coverts and tail-feathers slightly paler 

 slate-colour and inclining to pearly grey; crown of head black, 

 overspreading the hind neck towards the mantle; the under 

 surface of the body leaden-black, deepening on the throat and 

 chest ; thighs, sides of lower flanks, under tail-coverts, as well 

 as the under wing-coverts, white ; the lower greater coverts pale 

 pearly-grey like the quill lining ; axillaries leaden-grey ; bill 

 black ; feet reddish-brown. Total length, 9-5 inches ; oilmen, 

 1-25 ; wing, 8-4; tail, 3-15 ; tarsus, 0*6; middle toe and claw, 

 0-85. 



Adult Female. Similar to the male, but slightly paler in 

 colour. Total length, 9-6 inches; wing, 8'i. 



Adult in Winter Plumage. Distinguished by the white under 

 surface from the summer plumage, the forehead being white, 

 and the hinder crown and centre of the nape black, the feathers 

 having hoary-white margins ; sides of face, sides of neck, and 

 a collar round the hind- neck white, like the under surface of 

 the body. 



Characters. The adult Black Tern is easily recognised from 

 the other British species of Hydrochelidon, in summer plumage, 

 by its pale grey under wing-coverts, these being black in 

 H. leucoptera and white in JET. hybrida. The grey upper 

 tail-coverts and tail distinguish it from H. leucoptera, which is 

 black underneath, not dark leaden-grey as H. nigra is. From 

 H. hybrida it may be distinguished by its black bill and black 

 sides of the face. 



In winter plumage the three species are more difficult to 

 discriminate, but H. nigra and H. hybrida have the tail grey 

 and the rump also grey like the back, fJ. nigra is a smaller, 



