BRITISH WARBLERS 



previous year, and, ignoring all other opportunities of pairing, 

 await a happy reunion ? No one, I think, would suggest 

 that during all these months of wandering in the wilderness 

 they carry in their memory the image of a former mate, and 

 that when the sexual instinct develops at the proper season 

 this image becomes the central attraction, a goal that, at any 

 cost, must be attained. Would not one rather suggest that a 

 habit which had been formed in one season would be sufficient to 

 bring about continued pairing without attributing to the birds 

 any undue powers of recognition ? The whole question 

 resolves itself into one of expediency. Will Nature obtain the 

 best results if a male postpones pairing until the advent of 

 its former mate ? Let us consider the position of a male. It 

 arrives alone in the spring at its destination, and takes up its 

 former territory. And what then ? If it has no recollection 

 of a former mate, it must take the first opportunity that arises 

 of securing one, and will probably pair with the first female 

 that enters its territory. On the other hand, if the female 

 of the previous spring still occupies a place in its memory, 

 it must ignore all others, await its former mate that months 

 previously may possibly have been destroyed, and thus run 

 the risk of losing its chance of reproduction. While it is 

 difficult to see what advantage could be gained from the same 

 male and female pairing year after year, it is easy to see how 

 it might thus result in disaster. For us Nature has only 

 one purpose in view, namely, that the stronger individuals 

 shall meet, reproduce, and reproduce frequently. And here 

 we must bear in mind the law of territory. The male 

 that is capable of holding a territory and defending it from all 

 intruders is strong enough to reproduce, and the female that 

 is able to defeat her rival is also fit to reproduce. Automatic- 

 ally, therefore, the stronger individuals pair. An individual 

 that did not seize the first opportunity offered to it of pairing- 

 would not reproduce so frequently as one that did, and its 

 descendants, if they inherited a similar tendency to hesitation, 

 would gradually be eliminated. It would doubtless be untrue 



