Fertile Bird Hybrids 
Collared Dove (7. risorius) and these have bred 
again when paired with the red species. O. 
tranquebarica, although presenting a general 
similarity to the collared dove, is truly distinct, 
being much smaller, with a shorter tail, and dis- 
playing a marked sex-difference (the male only 
being red, and the female drab). Its voice is 
also utterly unlike the well-known penetrating 
and musical coo of the Collared Dove. 
There is a large class of fertile wild hybrids 
produced between forms differing only in colour, 
such as those between the Hooded Crow (Corvus 
cornix) and Carrion Crow (Corvus corone), the 
various species of JZolpastes bulbuls, and the 
Indian Roller (Covaczas indica) and Burmese 
Roller (C. affinzs). Indeed, it may be said that 
wherever two such colour-species meet they 
hybridize and become more or less fused. 
In this connection sportsmen, as mentioned 
by Darwin, performed unconsciously a most in- 
teresting experiment when, more than a century 
ago, they introduced largely into their coverts 
the Chinese Ring-necked Pheasant (Phaszanus 
torguatus) and the Japanese P. versicolor. Sofreely 
has the former bred with the common species 
already present there (Phastanus colchicus) that 
nowadays nearly all our English pheasants show 
traces of the cross in the shape of white feathers 
on the neck, or the green tinge of the plumage of 
the lower back. The influence of the Japanese 
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