110 Mr. Hugh Whistler on the 



The May birds are similar; both have paler bills than the 

 adult, with dusky tips. Mr. Whistler notes of the March bird 

 that '^ the ovary Avas minute at a time when most pairs had 

 eggs, and that very few of these white-bellied birds were to 

 be seen." I regard these two birds as young non-breeding 

 birds of the previous year. 



Similar to these last two is the Jane bird (763), which 

 undoubtedly is a non-breeding bird of the previous year, and. 

 represents a stage further on in the sequence of the plumage. 

 It, like the May birds, has an old brown crown, which is 

 being replaced by black, and is getting new white feathers 

 on the underparts ; wings and tail have just begun to 

 moult. Parts of this plumage are probably moulted again 

 about September, and the bird, getting the black belly, now 

 becomes fully adult. Details of this change are lacking, as 

 neither Mr. Whistler nor the British Museum has any 

 August or September birds ; but in a series of 52 birds 

 obtained from October to May, every month being repre- 

 sented by several specimens in the British Museum, no birds 

 are in any plumage but the adult plumage (with black crown 

 and belly and long streamers), except what are obviously 

 birds of the year (with brownish head edged with grey, 

 white underparts, and short streamers). Moreover, a late 

 bird from Burma on Nov. 19 in the British Museum shows 

 the last stage of this moult. 



765 is an interesting bird ; it is obviously fully adult, and 

 the black head and belly are being replaced by white feathers in 

 June, and the moult of wings and tail has just begun. Now 

 we know from the above that all, except birds of the year, 

 by Octoher have black crowns and bellies, so that this white 

 plumage can only be held for a short time, say two months, 

 and is moulted again. It may appear strange at first that a 

 Tern should assume breeding-plumage by October, breed in 

 March in that plumage, and then moult into ar.ort of eclipse 

 plumage about June and then into breeding-plumage again 

 by October ; and yet it is not so very startling when one 

 considers that when the Arctic Tern leaves us about Sep- 

 tember it has not yet assumed its winter plumage, and that 



