ARTIFICIAL COLOURING OF BIRDS 267 



species generally, or whether it occurs only in certain parts of 

 the forest district, and if so whether it is restricted to certain 

 individuals, and also whether it is permanently retained in 

 these. As it certainly does not take place on the attainment of 

 full maturity (as in the case of the above-mentioned ruminants), 

 it may well be termed senile melanism, with or without the 

 prefix local or individual. 



The experiments relating to melanism carried out by Mr. 

 Beebe on birds in the New York Zoological Park were con- 

 ducted on three species, and are described and figured in the 

 first number of Zoologica, a serial recently started by the New 

 York Zoological Society. The mean annual humidity of New 

 York is 73 per cent. ; but the average humidity of the chamber in 

 which the experiments were conducted was no less than 84 per 

 cent. During the warmer months the temperature averaged 68 

 degrees, or that of the city generally ; but from October to 

 March it varied from 60 to 72 degrees. 



The first experiment was conducted on a trio of young wood- 

 thrushes {Hylocichla mustelina), taken from the nest, and known 

 to be the offspring of normally coloured parents. One of the 

 trio died in an early stage of the experiments ; the second was 

 kept in a normal atmosphere, and differed in no respect from a 

 wild-bred bird ; while in the third, after a two years' sojourn in 

 the humid chamber, the black tips to the breast-feathers were 

 found to have become more than double the usual size. 



The second experiment was conducted on the white-throated 

 sparrow (Zonotrichia a/bicollis), of which two examples were 

 caught in the autumn of 1901, and one placed in a normal and 

 the other in a super-humid atmosphere. As in the other ex- 

 periments, the two birds had a precisely similar diet, from 

 which hemp-seed was excluded. In May 1902, the two sparrows 

 presented no noticeable differences ; but a year later a radical 

 change had taken place in the one kept in the humid chamber ; 

 the general effect being as though a dark veil had been drawn 

 over the normal markings, the whole tone of the plumage being 

 blackish, in place of the under-surface of the head and the 

 abdomen being almost white. 



The white-throated sparrow has a very extensive geo- 

 graphical range in eastern North America, but everywhere 

 presents the same type of colouring ; this lack of local variation 

 being probably due to its migratory habits, rendered necessary 



