to the places suitable for breeding. Why does the Reed-Bunting cling so tenaciously to an acre or more of marshy ground, while the Guillemot rests content with a few square feet on a particular ledge of rock? The answer is the same in both cases—to facilitate reproduction. But why should a small bird require so many square yards, whilst a very much larger one is satisfied with so small an area? The explanation must be sought in the conditions of existence. The Reed-Bunting has no difficulty in finding a position suitable for the construction of its nest; there are acres of waste land and reedy swamps capable of supplying food for large numbers of individuals, and the necessary situations for countless nests. But its young, like those of many another species, are born in a very helpless state. For all practical purposes they are without covering of any description and consequently require protection from the elements, warmth from the body of the brooding bird, and repeated supplies of nourishment. A threefold burden is thus imposed upon the parents: they must find food for themselves, they must afford protection to the young by brooding, and they must supply them with the necessary food at regular intervals. And their ability to do all this that is demanded of them will be severely taxed by the brooding which must perforce curtail the time available for the collection of food.
Let us then suppose that the Reed-Buntings
