385 



species with age, with sex, or with season. In some birds the 

 sexes are aUke, but the young different from either ; in others the 

 sexes are different and the young like the female. In some the 

 male during the nuptial season assumes brighter colours than 

 the female but is like her at other times ; occasionally he is adorned 

 with a crest or other long plumes found at no other period of the 

 year. It would be a very important fact if a case occurred at any 

 time in which the rule of the species, whatever it might be, was 

 not observed. For it would seem not always to be observed in 

 other countries. Thus Mr. Blyth has noticed that the ruff 

 (Machetes pugnax) is "tolerably common" in the vicinity of 

 Calcutta, " but never met with in breeding plumage."* This is a 

 remarkable circumstance, and its interest would be much increased 

 if in only a single instance a parallel case was met with, as regards 

 this species, in England. The ruff on the neck, by which the male 

 bird is distinguished in the breeding season, and from which it 

 receives its name, is notoriously variable in its colours, hardly being 

 found exactly alike in two individuals, and the same or similar 

 causes which bring about this variability, might possibly lead 

 occasionally to there being no ruff at all. 



Again in very many species, especially among the aquatic birds, the 

 summer and winter plumage differ considerably, and the degree of 

 difference seems to be dependent in some measure on the character of 

 the season. This question is of greater interest when we take the case 

 of migrants which are generally travelling at a time when this change 

 of plumage is taking place, and which may possibly be affected by 

 the climate or state of the weather in the countries it traverses in 

 its flight, especially if it stop to sojourn anywhere for a time before 

 resuming its journey.t For the change sometimes takes place veiy 



as also the influence of temperature, mentioned by the late Mr. E. T. Bennett, 

 in his edition of White's Selborne, p. 165, note 19. 



* Ann. and Mag. Nat. Hist , vol. 12 (1843), p. 170. 

 t See some remarks by myseK, many years ago, on the variation of 

 plumage in birds as afiected by climate, seasons, and other conditions, with 

 reference to a memoir by M. Gloger, in which he states he has " no doubt 

 that individuals of one and the same species of bird present different arrange- 

 ments of colouring, according to the climates wHch they inhabit, and that 



