274 Prof. R. Collett on the Occurrence 



of May 1869, shows how the change from winter- to summer- 

 plumage takes place. At the commencement this is effected 

 by the transformation of a portion of the winter-feathers, 

 while another portion of them is moulted. To these changes 

 are added (subsequently) new summer-feathers in the place 

 of those which have been cast^. On the other hand, a great 

 number of the brown and bleached feathers of the winter- 

 plumage still remain on the back. Their change into 

 summer-feathers is just commencing. This takes place by a 

 combination of shedding the margins and recoloration. The 

 margins, thinned and worn during the course of the winter, 

 are thrown off, whilst at the same time the white summer- 

 spots are developed from the above-mentioned greyish-white 

 patches inside the edges of the feathers. 



The recoloration takes place rapidly, probably in the course 

 of a few hours in each individual feather, and it is quite 

 exceptional to find feathers in the course of transformation. 



In the specimen last mentioned the head and the neck are 

 almost entirely in summer-plumage, with some (although 

 not full) gloss on the throat and neck-collars. The neck- 

 bars are still not perfectly developed. The nuptial plumage 

 commences to change into the third winter-plumage early 

 in the autumn. In one specimen from the neighbourhood 

 of Tromso (shot on the 22nd September, 1893) the first 

 winter-feathers had already commenced to appear on the 

 head and neck. In October and November specimens are 

 met with in transitional plumage, in which more or less of 

 the winter-plumage has been assumed. The change, however, 

 takes place rather irregularly. For example, in a specimen 

 in summer-plumage from Balsfjord (1892) the summer- 

 plumage was almost entirely retained on the 5th October. 

 This is probably a three-year-old individual (or perhaps still 



* One specimen of C. ylacialis, belonging- to the Stavanger Museum, 

 shot in Ryfylke the 15th June, 1889, is just in this somewhat later stage, 

 in which the back is filled with numerous half-grown and white-spotted 

 summer-feathers, which shoot up between the other winter-feathers 

 changed by recoloration. On the throat and the cheeks some loose white 

 winter-feathers are still found. 



