CARE OF OFFSPRING 233 



The significance of the striped coloration of nestling birds 

 will be discussed in Chap. XV., but there are other facts con- 

 cerning the development of highly coloured areas which may- 

 well be discussed here, even though the exact interpretation of 

 some is not yet known. 



The young of the Water-hen, for example, have the beak as 

 brilliantly coloured— vermilion and yellow — as in the adults, yet 

 by the time the first plumage of contour feathers has been de- 

 veloped this coloration has given place to a dingy green, and 

 so far this fact is inexplicable. But it is significant to note 

 that the young of the Great Crested Grebe {Podicepes cristatus) 

 when in its downy state has a vermilion-coloured, heart-shaped 

 patch of bare skin on the crown of the head, and of this there 

 is no trace in the adult. Has this red colour any special signi- 

 ficance? Perchance it is a "recognition" mark, enabling the 

 parents to find the young after they have dispersed into hiding 

 to avoid an enemy. Though this be so, it is hard to see why a 

 similar mark should not have been developed in other species 

 of Grebes. Again, young Coots in down have the forepart of 

 the face covered with small warty, or rather fleshy, papillae 

 exactly resembling the papillae on the face of the Pheasant, and 

 some other Game-birds, and these papilla, in the Coot as in 

 the Pheasant, are vermilion coloured, therein again, so far as 

 colour is concerned, resembling the young Grebe and Water- 

 heni 



Among the nidicolous birds bright colours occur around 

 and in the mouth. But these have an obvious purpose, inasmuch 

 as they serve as a guide to the parents when feeding their young. 

 In the Passerine birds the aperture of the mouth is made to ap- 

 pear abnormally large by the development on either side of the 

 gape of fleshy flanges, generally of a bright yellow colour. In 

 the young Jackdaw, which, be it noted, is hatched in dark 

 places, this flange is white, just as eggs laid in dark places are 

 white (p. 208), while in the Jay, Rook and Crow, for instance, 

 this flange is but feebly developed and is not brightly coloured. 

 But the most remarkable feature of this kind is the brilliant 

 coloration of the inside of the mouth. The colour varies, being 

 generally yellow, as in the young of Wagtails, Larks and 

 Thrushes, or purplish-red as in the Chaffinch. Sometimes, as in 

 the Hedge-sparrow, for example, the tongue and the roof of the 



