v THE PHILOSOPHY OF BIRDS’ NESTS 103 
ants’ nests, the soft materials of which they can easily hollow 
out. 
Many 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 tide- 
washed 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 débris 
of the shore, heaped together with as little order and con- 
structive 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 good, 
sometimes distinctly, sometimes more obscurely apparent, 
according as the habits of the species are more marked, or 
their structure more peculiar. It is true that, among birds 
differing but little in structure or habits, we see considerable 
diversity in the mode of nesting, but we are now so well 
assured that important changes of climate and of the earth’s 
surface have occurred within the period of existing species, 
that it is by no means difficult to see how such differences 
have arisen. Simple habits are known to be hereditary, and 
as the area now occupied by each species is different from 
that of every other, we may be sure that such changes would 
act differently upon each, and would often bring together 
species which had acquired their peculiar habits in distinct 
regions and under different conditions. 
