198 TERRITORY AND REPRODUCTION 



and on Horn Head ; and beyond this, to the 

 east, there are none, not even on the old rocks 

 that form the promontory of Inishowen. Why, 

 we ask, do countless numbers crowd the ledges 

 of Horn Head, whilst they are absent from the 

 precipices of Slieve League ; why, too, are they 

 absent from the granite cliffs of Owey ? The 

 reason is not far to seek. Either the face of 

 the cliff is made up of a series of broken 

 precipices, or the face of the precipices is 

 too smooth, or the otherwise suitable ledges 

 are situated too near the water, or the water 

 recedes from the base of the cliff at low tide. 

 Many miles of rock-bound coast are thus useless 

 for the purpose of reproduction. 



Now when we bear in mind how large an 

 expanse of coast is formed of blown sand or of 

 rocks of low altitude, and how many miles of 

 cliff fail to supply the three essential conditions 

 that we have been considering, we can see 

 that suitable breeding stations must be limited 

 both in number and extent. From a wide 

 expanse of ocean hosts of individuals are there- 

 fore obliged to converge at certain definite 

 points ; and hence, each recurring season, there 

 must arise a competition for positions at the 

 station, just as there is competition between 

 individual Buntings for positions in the marsh. 

 And the ability to obtain a position upon a 

 suitable ledge involves, in the first place, 

 an impulse to search for it ; in the second 

 place, an impulse to dwell in it ; and in the 

 third place, an impulse to resist intrusion 



