CONDITION ACCOMPANYING CHANGE 239 



which a bird displays in other species varies 

 not only at different seasons but even from 

 hour to hour. I have used the word " nature " 

 as equivalent to "interest," and I have spoken 

 of the bird's nature changing or altering accord- 

 ing to the circumstances in which it was placed. 

 But its nature is its inborn constitution, and its 

 constitution cannot change from day to day, 

 still less from hour to hour. So that, in a sense, 

 and having regard to strict scientific accuracy, 

 it is misleading in this particular connotation to 

 say that the bird's nature changes. 



What then does happen ? The instinct of 

 pugnacity must form just as much a part of 

 the hereditary make-up of the migrant, when 

 on migration, as when finally it reaches its 

 destination ; still more must it form part of 

 the constitution of the Bunting when it leaves 

 its headquarters temporarily and joins the flock. 

 And, if it is there, the question arises as to 

 why it does not respond. Now every instinct 

 requires for its response a stimulus of an appro- 

 priate kind, and, therefore, a reasonable view 

 to take would be that the necessary stimulus 

 was lacking. But this is a view which we 

 cannot uphold, because on all these occasions 

 an opposing male was present-^and, so far as it 

 is possible to judge by observation, that is the 

 stimulus which in the main evokes a hostile 

 response. We must therefore look elsewhere 

 than in its direction for a reason which will 

 adequately explain the behaviour. 



Though it be true that every instinct 



