238 4A THEORY OF BIRDS’ NESTS. 
exposed to view, no matter whether there is the most 
beautifully formed nest, or none at all. Kingfishers, 
which build almost invariably in holes in banks; 
Woodpeckers and Parrots, which build in hollow trees ; 
the Icteridee of America, which all make beautiful 
covered and suspended nests; and our own Wren, 
which builds a domed nest, are examples of the former ; 
while our Thrushes, Warblers, and Finches, as well 
as the Crowshrikes, Chatterers, and Tanagers of the 
tropics, together with all Raptorial birds and Pigeons, 
and a vast number of others in every part of the 
world, all adopt the latter mode of building. 
It will be seen that this division of birds according to 
their nidification, bears little relation to the character 
of the nest itself. It is a functional not a structural 
classification. The most rude and the most perfect 
specimens of bird-architecture are to be found in both 
sections. It has, however, a certain relation to natural 
affinities, for large groups of birds, undoubtedly allied, 
fall into one or the other division exclusively. The 
species of a genus or of a family are rarely divided 
between the two primary classes, although they are 
frequently divided between the two very distinct modes 
of nidification that exist in the first of them. 
All the Scansorial or climbing, and most of the 
Fissirostral or wide-gaped birds, for example, build 
concealed nests; and, in the latter group, the two 
families which build open nests, the Swifts and the 
Goat-suckers, are undoubtedly very widely separated: 
from the other families with which they are asso- 
