192 TERRITORY AND REPRODUCTION 



been first insured ? How could the supply 

 of food have been insured if numbers of the 

 same species had been allowed to breed in 

 close proximity ? 



From the foregoing facts it is clear that the 

 young of many species are at birth susceptible 

 to cold and unable to withstand prolonged 

 exposure. The parents must therefore be in 

 a position to obtain food rapidly, and conse- 

 quently it is important that there should be 

 an ample supply in the vicinity of the nest. 

 This end the territory certainly serves to 

 promote ; it roughly insures that the bird 

 population of a given area is in proportion to 

 the available means of subsistence, and it 

 thus reduces the risk of prolonged exposure 

 to which the young are always liable. 



This leads on to a consideration of those 

 cases in which the question of securing food 

 is subordinate to the question of securing a 

 station suitable for reproduction. 



I take the Guillemot as an example. In 

 principle its behaviour is similar to that of the 

 Bunting ; the male repairs to a definite place, 

 isolates itself, and becomes pugnacious. But 

 the Guillemot is generally surrounded by other 

 Guillemots, and the birds are often so densely 

 packed along the ledges that there is scarcely 

 standing room, so it seems, for all of them. 

 Nevertheless the isolation of the individual 

 is, in a sense, just as complete as that of the 

 individual Bunting, for each one is just as 



