BRITISH WARBLERS
degree of perfection in which we now perceive them, we shall find that the task is neither so simple nor so easy as it may at first appear to be. In a problem, too, of this description, it is well to remember that simple principles of explanation are to be preferred to complex, and in this instance a simple one is at hand, namely, that the imitations have been acquired by each individual during its own lifetime. How far is this explanation satisfactory? It is unquestionably true of a number of cases. The Blackcap replies to the "jug" in the Nightingale's song, repeats the song of the Redstart, or answers the "chuckle" of a Blackbird. In fact, numerous instances could be given of a member of one species producing an immediate representation of the song of one of another; but this is really unnecessary, since it is well known that birds kept in confinement have an innate proclivity for copying the sounds they hear. But this does not exhaust all the possible methods, neither do I think it explains all the phenomena with which we are brought face to face upon closer examination. There are some grounds for believing that part of the imitations may be congenital, the acquired imitation of the parent being transmitted to the offspring. Needless to say, the evidence I have hitherto been enabled to obtain bearing upon this point is far from being complete; a human lifetime is too short for the accumulation of the necessary facts; concerted observation on the part of a number of naturalists can only justify a conclusion, but I place it upon record, hoping that it may be the means of inducing others to investigate what I think may prove a source of knowledge so far as this much-debated controversy is concerned.
I have already mentioned that the colouring of the immature males on their arrival in this country in the spring is not so intense as that of the older birds, and that some of them still carry the brown-tipped feathers on their head; consequently, it is by no means a difficult matter to distinguish them. They are just as vigorous singers, although their song is not so perfect, and their power of imitation is considerable,
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