Page:Territory in Bird Life by Henry Eliot Howard (London, John Murray edition).djvu/267

Rh the nest, have been the main determining factors, and have led to a wide divergence in its function. At the one extreme the function is to insure a plentiful supply of food for the young; at the other, to insure a station suitable for rearing offspring. I took the Bunting and the Guillemot as types of the two extremes. The young of the former species are born in a very helpless state. They are susceptible to cold and unable to withstand prolonged exposure, and therefore it is essential that there should be an ample supply of food, upon which the parents can draw liberally, in the vicinity of the nest. But the nest is placed in a variety of situations, and accommodation in this respect may be said to be unlimited. The young of the latter species are not so susceptible to exposure, and moreover there is always an abundance of food in the waters beneath the cliff; but ledges of rock, upon which the egg can be securely deposited and the young successfully reared, are limited both in number and extent. The position then is as follows: there are situations in plenty in which hosts of Buntings can build their nests but the supply of food is a difficulty, and if the respective areas of different individuals were insufficient to supply them with the necessary food with the necessary rapidity, they would run the risk of losing their offspring and the species would not endure; on the other hand, cliffs upon which the Guillemot can rear' its young are limited, but the supply of food presents no difficulty, and consequently the