MONOGRAPH OF THE PETRELS. 



So many specimens are without any record of the date of capture, that it 

 is difficult to account for the variation with any certainty, but amongst those 

 specified, I find that the birds with pure white throats were obtained in May, June 

 and July, which are the winter months, while the black -throated birds were captured 

 in October and November, when the breeding season is approaching ; hence, I infer 

 that the changes of plumage are seasonal. In connection with the above change, the 

 black-throated birds also have an entirely black mantle, while in white-throated 

 specimens the feathers of the mantle have white bases. As the series before me 

 exhibits every possible intermediate gradation between the two phases, it is possible 

 that the change is accomplished without any direct moulting of the feathers of 

 the throat, and that the black spots, at first minute and occupying the tip of the 

 feather, gradually spread until the whole of it is black. 



Mr. Eagle Clarke (Ibis, 1906, p. 176) draws attention to the fact that adult 

 specimens obtained by the Scottish Antarctic Expedition in the Weddell Sea and 

 the South Orkney Islands presented two types of plumage. One of these, captured 

 in February, was probably an old bird in weathered plumage, and had a brown cast 

 over the black feathers, with white bases to those of the mantle ; in the second form 

 the bases were dusky, and the dark portion of the plumage was slaty-black ; while 

 a male taken in December was intermediate between the two. 



The chick, when five days old (January 18th, 1904), was slate-grey above, 

 paler and more sooty on the under side (Eagle Clarke, t.c). 



Young. According to Mr. Robert Hall the full grown nestlings were covered 

 with greyish down above, and greyish-white below, with the bill black. 



The bird described is in our collection, and the specimen figured is from 

 St. Ambrose Island, where it was obtained by Dr. Coppinger. 



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