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 ddbris 

 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. 



