206 TERRITORY AND REPRODUCTION 



which it first settled and which acts as a head- 

 quarters, it hunts through certain trees here or 

 certain bushes there and returns, and presently 

 it wanders away again, perhaps in another 

 direction, but, as before, works its way back 

 again to the headquarters. The journeys thus 

 radiate outwards from the headquarters, and 

 according to the success with which the bird 

 meets, so, probably, it happens that some trees 

 are searched more often than others and certain 

 directions are taken more frequently than others, 

 and by constant repetition a routine is estab- 

 lished which limits the direction and scope of its 

 wanderings. 



But in the case of the Guillemot the 

 conditions of existence are reversed : food can 

 be had in abundance but suitable breeding 

 stations are scarce. The few square feet of 

 ledge correspond to the tree or clump of bushes 

 which acts as a headquarters for the Warbler, 

 and the occupation of them is determined, as 

 it is in the case of the Warbler, by racial 

 preparation. Since, however, the ledge is only 

 made use of for the immediate purpose of 

 incubation and is in no way affected by 

 questions relating to food, there is no occasion 

 for the bird to wander along the ledge nor to 

 encroach upon those adjoining. Hunger stimu- 

 lates the Warbler to search the surrounding 

 trees, and so to extend its area ; but hunger 

 takes the Guillemot down to the water, and 

 hence the area which it primarily occupied 

 remains unmodified. 



