IN JERDON OR STRAY FEATHERS. 445 



colour gradually spreads over the entire back and scapulars, 

 and the black on the lower part of the back begins to 

 disappear, but very little change is perceptible in the wing. We 

 are inclined to believe that the change of colour in the wing 

 is also gradually assumed, and that the black disappears by 

 degrees, the grey colour making its appearance first on the 

 bases of the feathers, and extending bit by bit towards the 

 extremity of the quill. We may mention in conclusion that, 

 although it has been stated to the contrary, the Little Gull, 

 when immature, certainly has the tail perceptibly forked." 



984 bis.— Hydrochelidon leucoptera, Meisn. and 



Schintz. 



The Hydrochelidom, with their short, slightly-forked tails, 

 small feet and deeply emarginate interdigital membranes are 

 easily separable at any age from all our other Indian Terns ; 

 and the adults in full plumage of the three species of Hydro- 

 chelidon are not difficult to distinguish. 



Leucoptera has the head and neck all round black, and the 

 shoulder and greater part of the coverts of the wing pure 

 white. 



Nigra has the head and neck all round sooty black, and 

 the wings leaden grey. 



Eybrida has the top of the head and nape jet black ; lower 

 half of face white or nearly so, and wings leaden grey. 



But in the winter and immature plumages they are not 

 so easy to separate. 



Individuals vary so in size that it is not much use giving 

 comparative dimensions, but still, taking a good series, hybrida 

 will I think be found to be the largest, and nigra the smallest, 

 and the following may be taken, I believe, as approximate aver- 

 age dimensions of the three species : — 



Hybrida length, 11 ; wing, 9-5 



Leucoptera „ 10 ; „ 8*5 



Nigra „ 9; „ 8'0 



tarsus, 0-9 

 0-8 

 07 



The coloring of the soft parts, however, which seems to hold 

 good more or less even in young birds, affords one means of 

 discriminating fresh specimens : — 



Bill. Legs and feet. 



Hybrida blood red red. 



Leucoptera blackish, with a reddish tinge red. 

 Nigra black dark reddish brown. 



57 



