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Rh forward as something difficult of explanation, and many, perhaps, will doubt there being any such difficulty in regard to a thing so ordinary and commonplace. As to this, I can only say that I have arrived at a different conclusion.

What would be the ordinary way of accounting for such sudden and simultaneous taking to flight of a number of birds? One may suppose, in the first place, that a particular note is uttered by one or more of them on the espial of danger, and that this acts as a sauve qui peut to the rest. This seems a satisfactory explanation, but as against it, no such note is, as a rule, uttered, and even if it were, it would not account for all the facts as I have often observed them.

Day after day, and for hours at a time, I have watched these crowds of little birds under the circumstances described, and only on one single occasion was the sudden rising into the air in flight preceded by any note at all, nor did I observe anything—I do not believe there was anything to be observed—which could have frightened them.

In the one case referred to, which was different, "the flight was certainly preceded by a note—a very peculiar one, single, long, and remarkably loud, taking the size of the birds into consideration. It suggested somewhat the sudden blowing of a horn—though, of course, a small one. I could not tell which bird uttered it, but feel sure, from the quality of the tone, that it was a greenfinch. To the best of my observation, the note was uttered before the flight commenced, and the flight followed before it had ceased. Almost immediately afterwards I heard, for the first time, the caw of rooks, and my theory is (or was) that one of these,