THE PELICAN'S HORNS 325 



change under emotion very similar to our own, and 

 in some cases carried further, for our features at 

 least do not alter in shape ! The expansion of the 

 bare parts is said to be effected 07 the injection 

 of blood, but the pouches of the Adjutant and of 

 male Frigate-birds are air-inflated. 



In some birds, as in the Comb-Duck (Sarcidi- 

 ornis melanonota) and Sheldrake, the male assumes 

 a permanent fleshy outgrowth on the bill during 

 the breeding season, which is much reduced at 

 other times. In the American White Pelican (Pele- 

 canus erytbrorhynchus) a horny excrescence grows 

 upon the bill during the breeding season, and is 

 afterwards shed; it has been said to be confined 

 to the male, but the hen of the pair in the Zoo 

 at the time of writing has grown one for years past. 



The moult of the feathers has always attracted 

 attention ; in most birds it takes place once a 

 year, but in some, especially where there is a great 

 change of colour according to season, as in Ptarmi- 

 gans and the males of some Ducks, it occurs twice. 

 The quill-feathers, however, are only shed annually, 

 and generally in pairs, so that the bird's power of 

 fligh tis not importantly affected ; but in several 

 groups of water or marsh birds, which can take 

 refuge in water or on boggy land, all the quills are 

 cast together, so that the bird is flightless for some 

 weeks ; such groups are the Duck tribe (except 

 the Magpie-Goose), the Flamingoes, the Rails, the 

 Grebes, and the Cranes (except the Crowned Cranes 

 (Balearica)). 



