BRITISH WARBLERS
have an average chance of rearing offspring. There were, moreover, no females present; the responsibility for deserting the wood rested solely with the males who had preceded them, a fact which is of some importance, for the males take little if any share in the actual construction of the nest. How then was their decision arrived at? The question in this form savours too much perhaps of human process; let us therefore ask how the instinctive routine of activity was interrupted. Now it is probable that these males were either the same individuals, or the offspring of such, that nested in the wood the previous season, for instead of passing directly through it, as is customary with birds in search of new breeding grounds, they wandered restlessly about for some days before leaving, evidently expecting to find suitable territories. Hitherto the environment had answered their requirements, and the true course of their instinctive procedure therefore ran smoothly, but they were now called upon to face an experience which in all probability they had never met with before. I cannot, of course, prove that they had never been called upon to face this particular phase of experience, but bearing in mind the conditions of existence of these smaller migrants and the fact that this wood had only been inhabited by this species for the two previous seasons, it is not, I think, unreasonable to assume that some at least of these males had had no experience, so far as reproduction was concerned, beyond that which was supplied in those hundred odd acres. I am trying to show that for one or the other, or perhaps all, of these males, the environment could scarcely have acquired meaning as the outcome of previous experience, and that we cannot well call to our aid "meaning" in explanation of their behaviour. So that we are compelled to fall back upon racial preparation through the natural selection of variations of germinal origin, which is little enough help, for it is one thing to show how the reproductive instincts of this or that species have conformed to this or that environment through the elimination of the
6
