SOirOS OF BIRDS. 535 



some birds moult twice and thrice. The quill-feathers (rem- 

 iges) are usually shed in pairs, but in the ducks (AnatidcB) 

 they are shed at once, so that these birds do not at this 

 time go on the wing, while the males put ofE the highly- 

 colored plumage of the days of their courtship, and as- 

 sume for several weeks a dull attire. In the ptarmigan 

 both sexes not only moult after the breeding season is' 

 over into a gray suit, and then don a white winter suit, 

 but also wear a third dress in the spring. In the northern 

 hemisphere the males of many birds put on in spring 

 bright, gay colors. Other parts are also shed ; for example, 

 the thin, horny crests on the beak of a western pelican (Peli- 

 canus erythrorhynchus), after the breeding season, are shed 

 like the horns from the head of deer. Even the whole 

 covering of the beak and other horny parts, like those 

 about the eyes of the louffin, may also be regularly shed. 

 The variations in the frequency, duration, and completeness 

 of the process are endless. 



As a rule, male birds are larger and have brighter col- 

 ors, with larger and more showy combs and wattles than 

 the females, as seen in the domestic cock and hen ; and the 

 ornamentation is largely confined to the head and the tail, 

 as seen especially in male humming-birds. Mr. Darwin has 

 adduced a multitude of examples in his Descent of Man, 

 Vol. 2. Sometimes, however, both sexes are equally orna- 

 mented, and in rare cases the female is more highly colored 

 than the male; she is sometimes also larger, as in most birds- 

 of prey. There is little doubt that the bright colors of male- 

 birds render them more conspicuous and to be more readily 

 chosen by the females as mates, for in birds, as in higher 

 animals, the female may show a preference for or antipathy 

 against certain males. Indeed, as Darwin remarks, when- 

 ever the sexes of birds differ in beauty, in the power of sing- 

 ing, or in producing what he calls " instrumental music," 

 it is almost invariably the male which excels the female. 



The songs of birds are doubtless in part sexual calls or 

 love-notes, though birds also sing for pleasure. The notes of 

 birds express their emotions of joy or alarm, and in some 

 cases at least the notes of birds seem to convey intelligence- 



