Contributions to the theory of natural selection. A series of essays ... By Alfred Russel Wallace ...

242 A THEORY OF BIRDS' NESTS.
neck, and are very conspicuous. The sexes are exactly
alike, and the nest is in a hole of a tree.
8. Toucans (Rhamphastidae). These fine birds are
coloured in the most conspicuous parts of their body,
especially on the large bill, and on the upper and lower
tail coverts, which are crimson, white, or yellow. The
sexes are exactly alike, and they always build in a hollow tree.
9. Plaintain-eaters (Musophagidm). Here again the
head and bill are most brilliantly coloured in both sexes,
and the nest is in a hole of a tree.
10. Ground cuckoos (Centropus). These birds are
often of conspicuous colours, and are alike in both sexes.
They build a domed nest.
11. Woodpeckers (Picidoe). In this family the females often differ from the males, in having a yellow
or white, instead of a crimson crest, but are almost as
conspicuous. They all nest in holes in trees,
12. Parrots (Psittaci). In this great tribe, adorned
with the most brilliant and varied colours, the rule is,
that the sexes are precisely alike, and this is the case
in the most gorgeous families, the lories, the cockatoos,
and the macaws; but in some there is a sexual difference of colour to a slight extent. All build in holes,
mostly in trees, but sometimes in the ground, or in
white ants' nests. In the single case in which the nest
is exposed, that of the Australian ground parrot, Pezoporus formosus, the bird has lost the gay colouring of
its allies, and is clothed in sombre and completely protective tints of dusky green and black.