Contributions to the theory of natural selection. A series of essays ... By Alfred Russel Wallace ...

218 THE PHILOSOPHY OF BIRDS' NESTS.
the materials of a nest? Consequently, they all lay
in holes of trees, the tops of rotten stumps, or in
deserted ants' nests, the soft materials of which they
can easily hollow out.
Mlany terns and sandpipers lay their eggs on the
bare sand of the sea-shore, and no doubt the Duke of
Argyll is correct when he says, that the cause of
this habit is not that they are unable to form a nest,
but that, in such situations, any nest would be conspicuous and lead to the discovery of the eggs. The
choice of place is, however, evidently determined by
the habits of the birds, who, in their daily search
for food, are continually roaming over extensive tidewashed flats. Gulls vary considerably in their mode of
nesting, but it is always in accordance with their structure and habits. The situation is either on a bare rock
or on ledges of sea-cliffs, in marshes or on weedy shores.
The materials are sea-weed, tufts of grass or rushes,
or the dlebis of the shore, heaped together with as
little order and constructive art as might be expected
from the webbed feet and clumsy bill of these birds,
the latter better adapted for seizing fish than for
forming a delicate nest. The long-legged, broad-billed
flamingo, who is continually stalking over muddy flats
in search of food, heaps up the mud into a conical
stool, on the top of which it lays its eggs. The bird
can thus sit upon them conveniently, and they are
kept dry, out of reach of the tides.
Now I believe that throughout the whole class of
birds the same general principles will be found to hold