If then the Guillemot were to behave after the manner of the Bunting and assign to itself a portion of the face of the cliff, or if it were only to occupy a few ledges, or an even lesser area--a single ledge--what would be the result? That it would attain to reproduction is beyond question; that the egg would be safely deposited there can be no manner of doubt; neither is there any reason to suppose that the offspring would not be successfully reared. But, indirectly, its behaviour would affect the Guillemot race. For if it be true, as the crowded ledges certainly seem to show, that there is a dearth of suitable breeding ground, no greater calamity could befall the species than that some members should exercise dominion over too large an area of the habitable part of the cliff and thus prevent others from breeding. Under such conditions the race could not endure, since in this, as in every case, its survival must depend upon a close correspondence between the behaviour of the individual and the circumstances in the external environment. Scarcity of suitable cliffs is the principal reason of the ledges being so closely packed with Guillemots, just as it accounts for this part of the precipice being crowded with Kittiwake Gulls, that part with Herring-Gulls, and that part again with Razorbills and Puffins. Yet each individual preserves its few square feet of rock or soil from molestation, and the area each one occupies varies according to the conditions of existence of the species. Thus the Herring-Gull occupies a comparatively small area, although one many times larger than that of the Guillemot. It requires more space than the latter, owing to the fact that it not only builds a nest but rears four instead of a single offspring, and it can be allowed this, because, since its young remain in the nest until they are capable of sustained flight, it can make use of many miles of cliff from which the tide recedes at the base, or which have, at their base, rocks jutting out into the sea; but manifestly it cannot be allowed so much space as the Bunting.