114 BOMBAY DUCKS 
isolated from all other tribes. They show affinities 
to both bee-eaters and kingfishers, especially to the 
latter. Indeed, rollers are the terrestrial counterparts 
of kingfishers: they are kingfishers which do not fish. 
Both families are clothed in brilliant plumage, and 
in each the sexes are alike. Both nest in holes, and 
both lay white eggs. These last two characteristics, 
however, do not count for much as evidence of re- 
lationship, being merely the consequences of similar 
habits. 
It is almost a law of nature that those species of which 
both the cock and the hen bird are clothed in gay 
plumage lay whitish eggs and either nest in holes, or 
build covered nests. There are exceptions to the rule, 
which cannot be dealt with in this place. The reason of 
this general provision of nature is not far to seek, The 
hen, when she is sitting on her eggs, is liable to be 
attacked unawares by birds of prey; hence it is obviously 
to the interest of the species that she be as incon- 
spicuous as possible, unless, of course, she be a bird, like 
our universal friend the crow, fully capable of looking 
after herself, or like the king-crow, a real fighter. 
Thus it has come to pass that, in many species of 
birds, the hen is clothed in sombre plumage, even when 
the cock bird is arrayed, like Joseph of old, in a coat of 
many colours. It is, however, obvious that if a species 
nest in a hole, there is no necessity for the hen bird to 
be inconspicuous, hence among kingfishers, woodpeckers, 
rollers, and bee-eaters, which build in holes, both sexes 
rejoice in brilliant plumage. 
Again, if a bird nest in a dark place, it is important 
