26 Allen on an Inadequate “Theory of Birds' Nests." 
Wallace’s “ Theory of Birds’ Nests.” * This “theory” has for its 
basis the assumed “ law which connects the colors of female birds 
with the mode of nidification.” Mr. Wallace states it to be a rule, 
open to “but few exceptions,” “that when both sexes are of strik- 
ingly gay and conspicuous colors, the nest is ... . such as to conceal 
the sitting bird ; while, whenever there is a striking contrast of colors, 
the male being gay and conspicuous and the female dull and ob- 
scure, the nest is open and the sitting bird exposed to view.” He 
cites as examples of the first class, or those in which the female is 
conspicuously colored and the nest concealed or covered, “ six im- 
portant families of Fissirostres , four of Scansores t t\\Q Psittaci , and sev- 
eral genera and three entire families of Passeres, comprising about 
twelve hundred species, or about one seventh of all known birds.” 
This statement, however, proves on examination to be quite too 
sweeping, since a large proportion of the species here named either 
do not have a concealed nest, or are of sombre and obscure tints. 
There are also other entire families and various additional genera, 
in which the males are brilliantly and the females obscurely colored, 
which build a domed nest. I now propose, so far as the limits of a 
short article will allow, to test this theory by a rapid survey of the 
birds of North America, — an area certainly large enough to afford 
a fair basis of judgment. For this purpose I shall consider the 
modes of nidification under four heads, namely, (1) nidification in 
holes in trees ; (2) in burrows ; (3) domed, pensile, or otherwise 
more or less “ covered ” nests ; and (4) nests wholly open. 
1. Among North American birds those that habitually nest in 
holes in trees embrace several species of the smaller Owls, one or 
two kinds of small Hawks, all the various species of Woodpeckers, 
all the numerous species of Titmice of the genera Lophophanes and 
Parus, the several species of Nuthatches, the Brown Creeper, some 
of the Wrens, the Bluebirds (three species of Sialia), several species 
of Swallows, Martins, and Swifts, the Great-crested Flycatcher, the 
Carolina Paroquet, and three or four species of Ducks. In very few 
of these can the colors be considered as “ strikingly gay and con- 
spicuous,” and when this is the case, as in the Bluebirds, a few of 
* Originally published in the Intellectual Observer of July, 1867, and repub- 
lished with additions in 1870 in a collection of essays entitled “ Contributions 
to the Theory of Natural Selection,” and alluded to in more recent articles 
by the same author, including his recent paper on “ The Colors of Animals and 
Plants.” 
