THE PLUMAGE OF THE GREAT NORTHERN DIVER 141 



unsettled, but it is quite certain they are much later than 

 their cousins the Red-throated Divers (C. septentrionalis}. 

 These latter cast their primaries in early autumn, and are 

 clean moulted through by the middle of November. 



The Great Northern Divers are certainly several months 

 later, and I have an adult specimen killed in Orkney on 

 1 8th Feb. 1908, in which all the primaries and secondaries 

 are absent due to moult. I am inclined to think that these 

 birds probably cast their primaries sometime about the New 

 Year. During the process of the spring moult the birds 

 assume a strangely mottled appearance, due to the new black 

 feathers growing amongst the old mouse grey and white 

 feathers on the head and neck, and the back apparently 

 becomes wholly changed before the change in head and neck 

 is completed. 



The band across the vent appears to be moulted in or 

 about the middle of the change, and is practically entirely 

 lost for a short period, and is hardly distinguishable in 

 specimens killed in late February and early March. 



The following details respecting the individual feathers 

 in summer and winter are worthy of note. 



As already stated, the feathers in winter, covering the 

 whole of the dorsal region, are dark mouse grey, almost dull 

 black in colour, and there are hazy traces of two lighter 

 grey spots, corresponding in size and shape to the white 

 spots seen in the summer feathers. Fig. i represents a 

 winter feather taken from the interscapular region. Fig. 2 

 represents a summer feather from the same region, the colour 

 of which is glossy black, with two white spots, one on each 

 side of the rac/iis and near the end of the feather. 



Figs. 3 and 4 are respectively the winter and summer 

 feathers of the uropygium (rump), the remarks as to colour 

 being the same as for Figs, i and 2. 



It is worth noting, however, that the size' and shape of 

 the white spots on the summer feathers vary somewhat, 

 those on the feathers of the interscapular region (Fig. 2) 

 being more or less large and rectangular in shape, whilst 

 those of the rump and upper tail coverts are smaller and 

 round (Fig. 4). 



Fig. 5 represents a winter feather taken from the narrow 



