spicuous that they can hardly
be recognised as belonging to the same species.

_The Law which connects the Colours of Female Birds with the mode of
Nidification._

The above-stated anomaly can, however, now be explained by the influence
of the mode of nidification, since I find that, with but very few
exceptions, it is the rule--_that when both sexes are of strikingly gay
and conspicuous colours, the nest is of the first class, or such as to
conceal the sitting bird; while, whenever there is a striking contrast
of colours, the male being gay and conspicuous, the female dull and
obscure, the nest is open and the sitting bird exposed to view_. I will
now proceed to indicate the chief facts that support this statement, and
will afterwards explain the manner in which I conceive the relation has
been brought about.

We will first consider those groups of birds in which the female is
gaily or at least conspicuously coloured, and is in most cases exactly
like the male.

1. Kingfishers (Alcedinidae). In some of the most brilliant species of
this family the female exactly resembles the male; in others there is a
sexual difference, but it rarely tends to make the female less
conspicuous. In some, the female has a band across the breast, which is
wanting in the male, as in the beautiful Halcyon diops of Ternate. In
others the band is rufous in the female, as in several of the American
species; while in Dacelo gaudichaudii, and others of the same genus, the
tail of the female is rufous, while that of the male is blue. In most
kingfishers the nest is in a deep hole in the ground; in Tanysiptera it
is said to be in a hole in the nests of termites, or sometimes in
crevices under overhanging rocks.

2. Motmots (Momotidae). In these showy birds the sexes are exactly alike,
and the nest in a hole under ground.

3. Puff-birds (Bucconidae). These birds are often gaily coloured; some
have coral-red bills; the sexes are exactly alike, and the nest is in a
hole in sloping ground.

4. Trogons (Trogonidae). In these magnificent birds the females are
generally less brightly coloured than the males, but are yet often gay
and conspicuous. The nest is in a hole of a tree.

5. Hoopoes (Upupidae). The barred plumage and long crests of these birds
render them conspicuous. The sexes are exactly alike, and the nest is in
a hollow tree.

6. Hornbills (Bucerotidae). These large birds have enormous coloured
bills, which are generally quite as