sher makes its nest of the _bones_ of the fish
which it has eaten. Swallows use clay and mud from the margins of the
ponds and rivers over which they find their insect food. The materials
of birds' nests, like those used by savage man for his house, are, then,
those which come first to hand; and it certainly requires no more
special instinct to select them in one case than in the other.

But, it will be said, it is not so much the materials as the form and
structure of nests, that vary so much, and are so wonderfully adapted to
the wants and habits of each species; how are these to be accounted for
except by instinct? I reply, they may be in a great measure explained by
the general habits of the species, the nature of the tools they have to
work with, and the materials they can most easily obtain, with the very
simplest adaptations of means to an end, quite within the mental
capacities of birds. The delicacy and perfection of the nest will bear a
direct relation to the size of the bird, its structure and habits. That
of the wren or the humming-bird is perhaps not finer or more beautiful
in proportion than that of the blackbird, the magpie, or the crow. The
wren, having a slender beak, long legs, and great activity, is able with
great ease to form a well-woven nest of the finest materials, and places
it in thickets and hedgerows which it frequents in its search for food.
The titmouse, haunting fruit-trees and walls, and searching in cracks
and crannies for insects, is naturally led to build in holes where it
has shelter and security; while its great activity, and the perfection
of its tools (bill and feet), enable it readily to form a beautiful
receptacle for its eggs and young. Pigeons having heavy bodies and weak
feet and bills (imperfect tools for forming a delicate structure) build
rude, flat nests of sticks, laid across strong branches which will bear
their weight and that of their bulky young. They can do no better. The
Caprimulgidae have the most imperfect tools of all, feet that will not
support them except on a flat surface (for they cannot truly perch) and
a bill excessively broad, short, and weak, and almost hidden by feathers
and bristles. They cannot build a nest of twigs or fibres, hair or moss,
like other birds, and they therefore generally dispense with one
altogether, laying their eggs on the bare ground, or on the stump or
flat limb of a tree. The clumsy hooked bills, short necks and feet, and
heavy bodi