30 Allen on an Inadequate “Theory of Birds * Nests.” 
than counterbalanced by the readiness with which the nest itself 
is discovered. 
Not to do Mr. Wallace or his theory injustice, it may be added 
that he has instanced a considerable number of large families of 
birds, found outside of North America, in which the species nest in 
hollow trees, and in which both sexes do have “ surprisingly gay 
and conspicuous colors.” Among these are the Trogons, the Barbets, 
the Puff-birds, the Toucans, and the great group of Parrots and 
Paroquets. But Mr. Wallace has himself given an apparently far 
better reason for this method of nidification in some of these groups 
than that involved in his above-given theory, namely, that they have 
not the necessary “ tools ” for the construction of an elaborate nest. 
Most of them are weak-footed and sedentary, while in other cases 
the form of the bill renders the construction of a nest almost im- 
possible. Another large group, the species of which nest in holes 
in trees, are the Woodpeckers. Here an obvious and far more 
rational explanation is apparent than that afforded by the theory of 
concealment, for here the scores of dull-plumaged, sombre-colored 
species nest in holes just as do those that are conspicuously at- 
tired. In' this group the species do not seek cavities already at hand, 
as is the case in some of the groups just cited, but form them them- 
selves, and use them not only for purposes of nidification, but often 
more or less habitually as places of shelter. Nothing seems more 
natural than that they should avail themselves in this way of the 
advantages afforded them by their powerful chisel-shaped beaks, 
which they are constantly using as an abrading or “ digging ” organ 
in their search for food. The same explanation holds equally good 
for the plainly colored Tits that nidificate in holes that they them- 
selves have the power of forming. 
The Auks, Puffins, and some of the Guillemots are among the 
species I have cited as breeding in burrows. As they are species 
(occasionally conspicuous markings about the bill or head excepted) 
of neutral or obscure tints, — particularly as respects the exposed 
dorsal area of the sitting female, — their resorting to burrows is 
hardly necessary for concealment, since these species have no 
“ strikingly gay ” attire of plumage that would render the sitting 
bird in any case conspicuous. Such resorts, however, prove to be 
to them a great source of security, and give them an immense ad- 
vantage over other species of the same family that breed at the 
same localities with them, but in a wholly exposed manner. The 
