How Ptarmigans Molt''*' 



BY JONATHAN DWIGHT, Jr.. M. D. 



HESE widely distributed, circumpolar birds are a pleasing illus- 

 tration of the principle of protective coloration, even their 

 method of molt varying so from that of the other Grouse 

 as to adapt their plumages more perfectly to their surround- 

 ings. In winter we find them in snow-white dress, the Willow 

 and Rock Ptarmigans ( Laj^opi/s lat^opi/s and Lagopi/s nipcstris) 

 and their allies having jet-black tails which are nearly concealed by the 

 white coverts (Fig. <•). The White-tailed Ptarmigan {Lui^opi/s Icuciirus), 

 peculiar to the alpine tops of the Rocky Mountains, is absolutely white. 

 During the long Arctic winter the birds so blend with their snowy 

 environment as to be well-nigh invisible to their enemies, but with the 

 coming of the brief summer their white dress is no longer protective, as 

 they wander over the brown vegetation or gray rocks laid bare by the 

 sun. Now they must sit upon their eggs day after day in some warm 

 spot and presently care for their brood in latitudes where often in mid- 

 summer snow-drifts alternate with flowers. And so it is that a pre- 

 nuptial molt quickly covers the upper parts of their bodies and their 

 breasts with brownish or dusky mottled feathers that hide the white 

 wings and abdomen (Fig a). This molt occurs, usually in May, with 

 the melting of the snow, which. takes place earlier or later according to 

 latitude. 



After the duties of incubation are over, early in July, the postnuptial 

 molt, common to all species of birds, begins and it is completed in 

 about six weeks. The white wings and black tails (white in L. leu- 

 ciiri/s') are renewed and nearly all of the lower surface becomes white, 

 while upon the head, breast and back reddish or dusky feathers appear, 

 with mottling which is less bold than the nuptial and often reduced to 

 a mere sprinkling of darker color. Females, previously distinguishable 

 by coarser mottling, also don this dress, the preliminary winter plumage. 

 A supplementary postnuptial molt now follows so quickly that one 

 molt is often not completed before the other begins. The latter is 

 partial, but it involves those areas upon which dark feathers have grown, 

 they being now replaced by white ones. The overlapping of the molts 

 is shown by Fig. l>, where feathers of three stages of plumage may be 

 seen, the parti-colored effect being due chiefiy to the outbreak of molt 

 at various definite points from which new feather growth, as in other 

 species, regularly radiates along definite paths. 



The purpose of the preliminary plumage, apparently, is to tide the 

 birds over the autumn or, rather, the brief period that in Arctic regions 



*See also an important paper on this subject by Dr. Dvvight in 'The Auk' for April, 1900. 



(175) 



