ARTIFICIAL MODIFICATIONS IN THE 

 COLOURING OF BIRDS 



By R. LYDEKKER 



During the last few years a number of experiments have been 

 undertaken in America by Mr. C. W. Beebe, of the New York 

 Zoological Society's Gardens, with a view of ascertaining the 

 amount of alteration which can be effected in the colour or 

 colour-pattern of the plumage of birds by means of conditions 

 of temperature and humidity differing more or less markedly 

 from the normal. The results are not only remarkable, but of 

 great interest and importance with regard to the origin and 

 stability of local forms and species, and consequently on what 

 amount or kind of variation ought to be recognised as of racial 

 or specific value. A further series of experiments has been 

 instituted with a view of ascertaining the effect on the nuptial 

 plumage by keeping birds under somewhat abnormal conditions, 

 and especially by preventing their breeding. 



In regard to the experiments dealing with the effects of 

 humidity, it is a well-known fact that many kinds of terrestrial 

 vertebrates inhabiting warm, moist districts display a much 

 darker type of pigmentation in their hair, feathers, or scales 

 than is the case with individuals of the same or kindred species 

 dwelling in drier localities. Correlated with this darkening of 

 the epidermal covering is frequently a difference in the matter of 

 size, extending in some instances to the entire body, but in other 

 cases restricted to some particular region, as exemplified by the 

 lengthening or shortening of the tail and wing feathers in birds. 



When the dark humid forms are isolated by barriers of 

 some description from their normal representatives, they are 

 invariably recognised by naturalists as distinct species or races, 

 according to the degree of differentiation shown ; while even 

 in cases where a gradation can be traced from the normal to 

 the melanistic phase, each extreme type of the series (as well 

 as sometimes a certain proportion of the intermediate stages) 

 is admitted to be worthy of recognition by the systematist. 



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