ORIGIN AND CHARACTERISTICS 27 



are later in their moult than adults, and in a 

 great many cases the first set of quills are re- 

 tained during the first year of existence, although 

 in not a few Gallinaceous birds, which are able 

 to fly before fully grown, new sets of quills are 

 acquired as maturity is reached. Among birds 

 that moult very slowly, or that are in a chronic 

 state of plumal change, may be mentioned the 

 Swifts, the Birds of Prey, the Herons, and the 

 Ptarmigan. With the exception of the latter, 

 which by the way dons no less than three 

 distinct plumages in the year, all these birds 

 appear to be moulting their wing quills very 

 slowly throughout the year save perhaps in the 

 breeding season. Some of this change of colour, 

 due to season, is produced by an actual change 

 of pigment and not by a replacement of the 

 feather. (Conf. Stray Feathers, p. 154, for ad- 

 ditional details respecting the moulting of birds.) 

 Before leaving this portion of the subject we 

 may briefly allude to another periodical change 

 which takes place in the integument .of certain 

 birds. This relates to the peeling or shedding 

 of the claws in some of the Grouse during 

 spring, the elongation of the bill in the Redpoles 

 during summer (possibly due to a change of 

 food), the shedding of a horny projection from 



