THE LIFE-HISTORY OF BIRDS 279 



known that whereas in many birds this ecdysis takes place 

 but once annually, in others, a second, more or less complete 

 change of feathers take place during the year ; while in some 

 exceptional cases even a third moult may take place. 



It is highly probable that among the more primitive birds 

 three or four moults annually were the rule; and that the 

 number became reduced as the feathers gained increased per- 

 fection and ability to withstand the wear and tear of life. 

 Moreover, the development of new feathers entails a serious 

 drain on the system, to which domesticated birds, at any rate, 

 not infrequently succumb. 



So far as the known facts go, it would seem, and this is 

 significant, that birds which have reached, approximately, their 

 maximum in the matter of brilliancy of plumage, moult but once 

 annually ; as, for example, in Kingfishers, Parrots, Passerine 

 birds ; the Swans and Geese among the Anatidae ; the Gulls 

 among the Great Plover tribe ; the Cranes and Bustards ; the 

 Birds of Prey ; Steganopodous birds and Storks, Petrels and 

 Struthious birds. This list of course might be greatly extended, 

 though, doubtless, many exceptions will be found on further 

 investigation to have been included in those given herewith. 



Where this maximum has not been reached, the more or 

 less gaily coloured dress is exchanged for a longer or shorter 

 period for a duller dress, which is assumed by a moult. 



Since, whatever the number of moults, the quills are shed 

 but once annually, two kinds of moult are distinguished — com- 

 plete and partial. The former takes place after the breeding 

 season, but the period of the latter is not so fixed. As a rule, 

 it takes place just before the breeding season, when a special 

 nuptial dress of bright colours is assumed, as in the case of a 

 large number of the Plover tribe. Among the Ducks, where 

 the sexes differ in plumage, both sexes undergo the usual com- 

 plete moult after the breeding season, the new plumage in both 

 being dull. In the autumn, however, the male assumes what 

 answers to the " nuptial " dress of the Plover tribe, as we have 

 already remarked, and this does not appear to undergo any 

 heightening of colour as the critical period of courtship begins. 

 But in many brightly coloured species which now have but a 

 single, post-nuptial moult, a very pronounced brightening up 

 of the plumage takes place in the spring, not, however, be it 



