224 WARFARE BETWEEN DIFFERENT SPECIES 



Warbler is not the only bird that acts as a 

 stimulus to the instinct of the Blackcap ; 

 Whitethroats are often attacked, and the Chiff- 

 chaff is a source of irritation. Even when a 

 male Blackcap is engaged in incubation, it will 

 leave its nest on the approach of a Chiffchaff, 

 and, having driven away the intruder, proceed 

 to sing excitedly. At other times both male 

 and female will combine to attack this small 

 intruder. 



But this does not mean that the Chiffchaff 

 suffers persecution ; it is itself most aggressive, 

 as is shown by the fact that it will join in the 

 Blackcap quarrels and attack the combatants 

 indiscriminately. Its behaviour, however, re- 

 quires further consideration, especially as regards 

 its relations with its nearest of kin — the Willow- 

 Warbler ; for here we have a mutual intolerance 

 which is somewhat remarkable, and evidence of 

 it can be found wherever the birds occupy the 

 same ground. Now it can be observed that the 

 hostihty is not limited merely to occasional acts 

 of intolerance, but that there is organised 

 warfare lasting, it may be, for many days in 

 succession, and that the actions of the birds bear 

 the stamp of a persistent striving towards some 

 endi On one occasion the Willow- Warbler 

 may be the aggressor, on another the Chiff- 

 chaff, and at times it is difficult to say which of 

 the two is responsible for the quarrel. In size 

 and in strength they are equal, and the " will to 

 fight " is as strong in the one as in the other, so 

 that it is seldom, if ever, possible to point to 



