386 



rapidly. Mr. Yarrell mentions the case of a common black-headed 

 gull in the Zoological Gardens, in which the change of colour on 

 the head from white to dark brown in the spring was completed in 

 five days ; " it was a change of colour, and not an act of moulting, 

 no feather was shed." * Some light might be thrown by the local 

 faunist upon this subject, as also upon the still larger question of 

 species generally, especially when established upon slight differences 

 of plumage only, if those in which any of the above particularities 

 were conspicuous were compared with the same or closely allied 

 species obtained in other localities in England or abroad at the 

 same seasons of the year, and if this were done for several years in 

 succession. By close comparison of specimens in this way many 

 formerly supposed species among the waders and swimmers are 

 now recognized as mere varieties of others, or different states of 

 plumage dependent upon season or other circumstances. Also 

 among our land birds, we know that there are many other European 

 species closely allied to some of them, and it would be important 

 to note if in any of our home specimens we ever found an approach 

 to the slight variations of character by which some of these 

 foreigners are distinguished, or any thing intermediate that tends 

 to bring them together.f That many local races or sub-species 

 only retain their peculiarities and distinctness from other nearly 

 allied forms, so long as they are confined to their own locality, 

 seems shown by the remarkable circunistance mentioned by M. de 

 Selys-Longchamps, that the Cisalpine sparrow, when transferred to 

 Paris and made to build there, had for its progeny the common 

 house sparrow. J But in fact the whole question as to the light in 



one and the same individual, amongst the birds of passage, changes during 

 nearly the whole year the colours of its plumage, according to the different 

 climates through which it passes." — Mag. of Zool. and Bot., vol. l,pp. 24-25. 

 Mr. Gould, too, has remarked " that birds from the central parts of con- 

 tinents are always more brilliantly coloured than those inhabiting insular or 

 maritime countries. He attributes this principally to the greater density and 

 cloudiness of the atmosphere in islands and countries bordering the sea."— 

 Ann. and Mag. Nat. Hist., vol. xvii., p. 510. * Brit. Birds, vol. iii., p. 438. 

 t See remarks " on the variation of species," with reference to many very 

 closely allied European species of birds. — Eep. Brit. Assoc, Cheltenham 

 meeting in 1856. Trans, of Sect., pp. 103-4. X Faune Beige, p. viii. 



