• We have no idea how these callow travellers find
their way, but the young cuckoo—and the point is very important— has an overwhehning inner compulsion to flysomewhere, anywhere—in autumn. I discussed this at great length years ago with Mr. Benjamin Kidd, an acknowledged authority, on evolution. He had a tame young cuckoo which had, the liberty of his study. It would come to his call and apparently enjoyed its captivity; butwhen September
came a strange mood fell upon it, in fits. It rested motionless except for a very slight rhythmic vibration of the wings almost like breathing ; and when the mood was on it, nothing else entered its consciousness. It was quite deaf to its master's call. This happened only when autumn came and only at night. This single instance, which I quote not for the first time, seems to me to establish two facts that the latest authorities have underestimated. Birds are driven by an inner impulse, independent of food or temperature, and the impulse works at a definite time of day as well as a definite time of year. It does not, of course, touch the question of the directional sense. Of that so far we have no hint. But Mr. Benjamin Kidd's study, where the young cuckoo migrated in spirit through the autumnal night, should be a locus classicus.
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