26 Allen on an Inadequate "Theory of Birds Nests." 



Wallace's " Theory of Birds' Nests." * This " theory " has for its 

 basis tlie 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 oi Fissirostres, four oi Scansores,i\\e Psittaci, and sev- 

 eral genera and three entire families of Passeres, comprising about 

 twelve hundred species, or abchit 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 Lopliophanes 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." 



