254 WARFARE BETWEEN DIFFERENT SPECIES 



individual, the two questions we set ourselves 

 to examine in this chapter were : Is there any 

 circumstance in the life behaviour of the 

 individual with which the hostility can be 

 definitely related ; and, will the hostility lead 

 to the securing of a greater measure of success 

 in the attainment of reproduction ? 



Many different species assemble together in 

 winter and roam from place to place in search of 

 food. But in spring their behaviour undergoes 

 a remarkable transformation ; they avoid one 

 another and become quarrelsome, so much so 

 that whereas the outstanding feature of the 

 winter is sociability, that of the spring is 

 hostility. With this general fact before us, 

 we proceeded to investigate this change of 

 behaviour still further. First of all we took 

 the case of a migrant, and, comparing its 

 behaviour, as it journeyed, with that when 

 finally it reached its destination, we found 

 that the bird which was notoriously pugnacious 

 when in occupation of a territory betrayed no 

 interest in other species as it travelled to the 

 accustomed breeding ground. Not only so, but 

 even though it was attacked, we found that 

 its pugnacious instinct still failed to respond. 

 Here, however, it may be contended, and with 

 reasonable justification, that in the interval 

 which elapses before the ultimate destination 

 is reached, some change in the organic con- 

 dition of the bird may occur which will account 

 for its altered behaviour ; or, it may be urged, 

 with no less justification, that whereas on 



