COLOUR-CHANGES WITHOUT MOULTING 161 



in the case of those species where the old mdividuals are not 

 subject to such a change of colour at all, e.g. the Falcons and Gulls ; 

 and, on the other hand, that in the case of many young birds this 

 alteration takes place on parts of the body in which, in old indivi- 

 duals, the change to the breeding plumage is effected not by altera- 

 tion of colour, but by moulting. This is the case in several of the 

 Plovers, among other species. 



Among the Falcons, it has been in the case of only one species — 

 the Merlin — that I have noticed an alteration of colour in its first 

 spring ; but the material at my command has been so abundant, 

 and my observations have extended over so many years, that every 

 doubt as to their accuracy is out of the question. These young 

 Falcons are met with here on migration in the course of April 

 and at the beginning of May. At that time the colour-changes are 

 about half completed, and may be observed most clearly in the 

 feathers of the backs of male birds. The dusky earthy brown colour 

 of these feathers passes into a dark slate grey, which is first 

 discernible as blackish streaks in the lines of the shafts, and soon 

 spreads over the whole of these feathers, supplanting, as it does so, 

 the rusty grey spots along their margins. Simultaneously a lively 

 rust-red tint makes its appearance at the back of the neck : the 

 crown of the head assumes a very dark blackish slate-grey colour, 

 and here and there feathers on the upper and lower breast become 

 faintly rust-coloured. The colour of the back of such individuals, 

 however, never attains to the beautiful pure blue grey of the old 

 birds, but remains a dull bluish slate-grey. 



Of the Gulls I have had under my observation large numbers 

 of the Herring Gull, the Great Black-backed Gull, and Lesser Black- 

 backed Gull. In old birds of these species, the only parts of the 

 plumage subject to changes of colour are on the head and neck. 

 In the winter plumage the ground colour of these parts is white, 

 but is marked by greyish brown streaks. In the spring, however, 

 this plumage, by an alteration of colour, is changed to a pure 

 white. 



In young birds the plumage is, up to their second spring, dull 

 white, with blurred, light-brown markings ; subsequently, by an 

 alteration of colour, their plumage acquires a more or less perfect 

 resemblance to that of their parents. In the case of the Herring 

 Gull, the bluish grey coloration at first spreads over scattered 

 feathers of the plumage of the upper parts, their light-brown colour 

 disappearing at the same time. The light-brown markings like- 

 wise disappear on the head, neck, ixnd lower parts, the feathers of 

 which become white, though not as pure white as those of the old 

 birds. 



