144 ANNALS OF SCOTTISH NATURAL HISTORY 



(a) That the first feathers to show signs of the spring 

 moult are those of the interscapular region. 



(/;) That the feathers which cover the head and neck 

 are the last to become completely changed. 



(c) That all the flight feathers are dropped simultaneously 



and not in pairs, and that therefore the divers as 

 well as the ducks are deprived of the power of 

 flight during a short period of moult. 



(d) That the period of the spring moult spreads over 



a considerable area of time, but that, roughly 

 speaking, it commences in December and becomes 

 complete in May, a period ranging through five 

 months of the year. 



Referring again to the specimen already mentioned as 

 having been shot on i 8th February in Orkney, and as having 

 no flight feathers owing to moult, I have already expressed 

 an opinion that the Great Northern Diver moults the 

 primaries much later in the year than the Red-throated 

 Diver. Furthermore one would reasonably expect the 

 primaries to be moulted during the autumn moult. 



Clear it is, that I have a specimen moulting its primaries 

 during the spring moult. The question which naturally 

 arises from this specimen is. Are the Great Northern Divers 

 analogous to the Ducks in this respect ? e.g:, as Mr. Bonhote 

 has pointed out, in the Mallard the primaries are moulted 

 immediately after the assumption of the " eclipse " plumage, 

 and then, in a week or two, the assumption of the winter 

 plumage starts. If this is so, the winter plumage of the 

 Great Northern Divers is analogous to the " eclipse " plumage 

 in the Ducks and the primaries are moulted immediately 

 after the full winter plumage is assumed. 



It must, however, always be borne in mind, in dealing 

 with cases which appear out of the ordinary, that there 

 may, very possibly, have been some physical debility in the 

 particular specimen under notice, which may account for the 

 apparently protracted or retarded moult. This may possibly 

 be the explanation of my specimen being minus the flight 

 feathers in the middle of February. The case is interesting, 

 and further evidence on this and other matters raised in this 

 article would be very welcome. 



