unlikely that there should be a leader, and both this and the other explanation, which at first sight seems satisfactory, are destroyed by the salient fact that in hardly any case do all the birds rise and fly away together, but only the great majority. Almost invariably a certain number of them, though sometimes only half-a-dozen or so, or even less, remain, nor has this anything to do with the particular species of bird. Moreover, the flying up of any bird from the crowd does not, of itself, communicate alarm to the others, for first one and then another and often several at a time may constantly be doing so, whilst the rest feed quietly and take no notice. It may be said that it is only when a bird flies off in alarm that its flight communicates alarm to its companions. That it does so necessarily, even in such a case, I, from general observation, very much doubt, and also, if the facts as I have given them be a little considered, it will be seen that the difficulties are not met by this view of the case.
The theory of a leader seems more applicable to birds like rooks, which are gregarious, and may be constantly watched in large numbers together, without the intermixture of any other species. The same difficulties, however, apply here, and even to a greater extent, for the movements of rooks are more complicated, whilst alarm or any such primary impulse as the origin (I do not say the explanation) of them, is in most cases quite out of the question. An instance or two of these sudden and quite simultaneous movements of bodies of rooks I have noted down directly after observing them. They would be much in place here, but as I have two chapters devoted to these birds, and, more-
