COLORATION 109 



or "fledgeling" plumage, commonly answers to an ancestral 

 plumage is surely borne out by what is displayed in the 

 case of the young of the great titmouse {Parus major) 

 and the grey titmouse (P- cinereus). With the general 

 appearance of the first named my readers must be famihar 

 enough, for it is a common British bird. Suflfice it to say 

 that its coloration is a combination of blue, black, yellow, 

 and white. The grey tit, on the other hand, though 

 precisely similar in tte pattern of the coloration, differs in 

 the hue thereof, pearl grey taking the place of blue, and 

 white of yellow. The fledgeling great tit, it is next to be 

 noticed, differs from the adults — both sexes being coloured 

 alike — in being duller in hue as to the blue and yellow, 

 while the white of the face is strongly tinged with yellow, 

 and the black lacks the metallic lustre, and is less in area, 

 being absent on the side of the neck and breast. Now, 

 the fledgeling grey tit is practically indistinguishable from 

 the young great tit of the same age, from which we are 

 surely justified in regarding the grey tit as a derivative of 

 the great tit. The loss of the yellow colour by the adult 

 grey tit has thereby made two species where originally 

 there was but one. Yet other and similar cases could be 

 cited, but this will surely suffice, while it will also serve 

 to attest the value of a study of nestling birds as a guide to 

 the lines of evolution which their parents have followed. 

 A broad, general, survey has now been given of some of 

 the more important features which have been brought to 

 light by a study of the coloration of nestling birds : but 

 certain puzzling phenomena have been purposely left out 

 of account till now. And this because they represent 

 isolated facts, in most cases at any rate of doubtful mean- 

 ing. They have to do, in short, with the development of 

 ornaments in nestling birds, or with the development 



