CONDITION ACCOMPANYING CHANGE 233 



each, as far as it is able, will resist intrusion on 

 the part of other species. 



Now the southern end of the Common is 

 always inhabited by individuals belonging to 

 one of these species, or to others of close 

 affinity ; so that wherever these travellers settle 

 whilst passing across it, the chances are that 

 they will find the ground occupied — and their 

 behaviour under such circumstances is no less 

 interesting than the behaviour of the bird upon 

 whose ground they are trespassing. We will 

 take the case of the Whinchat. It arrives from 

 the south-west, and, flying from bush to bush, 

 works its way in a north-easterly direction. In 

 doing so it intrudes > upon the territory of 

 a Stonechat ; and the Stonechat, becoming 

 excited, flies towards it, and it retires for a short 

 distance in the direction from whence it came. 

 Here again it is followed and attacked and 

 again moves on, and then, flying in a circle as if 

 to avoid the territory which blocked the path, 

 resumes its former line of flight, though still 

 followed by the Stonechat, which after continu- 

 ing the pursuit for perhaps a quarter of a mile, 

 suddenly turns in the air and returns to its 

 headquarters. 



It is difficult to put oneself in the place of 

 the Stonechat or of the Whinchat. But even 

 after making due allowance for the danger 

 inseparable from any attempt to do so, there 

 remains the unquestionable fact that whereas 

 the impulse to attack was strong in the one, the 

 impulse to defend itself was wholly lacking in 



