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. Automatically, 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
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