160 THE STRUCTURE AND LIFE OF BIRDS chap. 



attributes the change not to a breaking off of the 

 edges, but to a peeling of the barbules. However this 

 may be, he must surely be right when he maintains 

 that in spring there is a rounding off of the ragged 

 edges of feathers. The Linnet's nuptial plumage 

 would be but a sorry garb if the dropping away of the 

 edges left what remained all ragged. A far more 

 remarkable cause of change of colour is the entrance 

 of fresh colouring matter into the feather, which can- 

 not therefore be an entirely dead thing. This is what 

 takes place when the Blackheaded Gull puts on his 

 spring head-dress, the colour, according to Gatke, 

 appearing first at the edges of the feathers and 

 gradually extending till the whole is dyed. In winter 

 the breast of the Dunlin is almost white, in spring it 

 becomes black, the pigment working its way to every 

 part of the feathers through channels as yet un- 

 discovered. By a similar process the head of the 

 Little Gull changes in spring from white with a dash 

 of ashen-gray to black. As in the Linnet in captivity, 

 so in the Herring Gull there takes place a withdrawal 

 of pigment, for the head having been gray in winter 

 becomes snow-white in spring. In these cases no 

 indication of moulting, such as half-grown feathers, is 

 ever found. The plumage of the Wood-sandpiper is 

 an interesting study, since it supplies an example of 

 the influx of fresh colour into the feathers and also of 

 the rounding off of ragged edges. Birds in captivity 

 sometimes show these changes well. This year the 

 Knots at the Zoological Gardens appeared with the 

 chestnut-coloured breasts proper to them in spring, 

 but whether the change in their case is due to the dull 



