"Of the two assemblies on the ground, one is in perpetual motion, birds constantly rising—either singly, in twos or threes, or in small parties—from where they were, flying a little way just above the heads of their fellows, and re-settling amongst them again. Thus no individual bird, as it seems to me, remains where it was for long, though those in the air, at any given moment, form but a small minority, compared with the main body on the ground.
"But the birds composing the other great assemblage keep their places, or, if some few rise to change them, these are not enough to give character to the whole, or even to attract attention. It is curious to see two such great bodies of birds close to each other, and on the same uniform pasture-land, yet behaving so differently, the one so still, the other in such constant activity.
"About 4 P.M. a great number of rooks rise from some trees in a small covert near by, and fly towards those on the ground. As they approach the first great body—which is the lively one—the birds composing it rise up, as with one accord, and fly, not to meet them, as one might have expected, but in the same direction as they are flying. So nicely timed, however, is the movement, that the rising body become, in a moment, the vanguard of the now combined troop.
"All these birds then fly together to the other assembly, and whilst about half of their number sweep down to reinforce it, the other half continue to fly on. The flying rooks, however, are not joined by any of those on the ground. How curious it is that, in the first instance, the one whole body of birds does the same thing instantaneously, and as by a common impulse, whilst in the second, half acts in one way, and half in another, each appearing to have no doubt or hesitation as to what it ought to do! Again, how different is the conduct of the two field-assemblages. One rises, as with one thought, to join the flying birds. The other, as with one thought, remains standing. Unless, in each case, some signal of command has been given, then what a strange community of feeling in opposite directions is here shown. Where is the individuality that one would expect, and what is the power that binds all the units together?
"Are rooks led by an old and experienced bird?—which is, I believe, the popular impression, as embodied in a famous line of Tennyson, for which one feels inclined to fight. At first sight, the rising of a whole body of rooks (or any other birds) simultaneously, either from the ground or a tree, might seem to be most easily explained on the theory of one bird, recognised as the chief of the band, having in some manner—either by a cry or by its own flight—given a signal, which was instantly obeyed by the rest. But how—in the case of rooks—can any one note be heard by all amidst such a babel as there often is, and how can every bird in a band of some hundreds (or even some scores) have its eyes constantly fixed on some particular one amongst them, that ought, indeed, on ordinary physical and mechanical principles, to be invisible to the greater number? If, however, to meet this latter difficulty, we suppose that only a certain number of birds, who are in close proximity to the leader, see and obey the signal, and that these are followed by those nearest to them, and so on till the whole are in motion, then two other difficulties arise, neither of which seems easy to get over. For, in the first place, the birds do not, in many cases, appear to rise in this manner, but, as in the instances here given, simultaneously, or, at least, with a nearer approach to it than any process of spreading, such as here supposed, would seem to admit of; and secondly, it is difficult to understand how, if this were the case, any bird—or, at least, any few birds—could fly up without putting all the others in motion. Yet, as I have mentioned, birds in twos or threes, or in small parties, were constantly rising and flying from one place to another in the assemblage of which they formed a part, whilst the vast majority remained where they were, on the ground. This fact offers an equal or a still greater difficulty, if, dismissing the idea of there being a recognised leader, we suppose that any bird may, for the moment, become one by taking the initiative of flight, or otherwise. And even if we assume that any of these explanations is the correct one, in the case of a whole body of rooks taking sudden flight, or directing their flight to any particular place, or with any special purpose, what are we to think when half, or a certain number of the band does one thing, and the other half another, each, apparently, with equal spontaneity? We are met here with the same difficulties—and perhaps in a still higher degree—as in the case of the flocks of small birds at the stacks in winter.
"If rooks follow and obey a leader, one might expect them to do so habitually, at least in their more important matters. The flight out from the roosting-trees in the morning, and the flight into them again at night are—when it is not the breeding-season—the two daily 'events' of a rook's life. Here, then, are two subjects for special observation.
"November 30th.—At 3 P.M. I take up my position on the edge of a little fir-plantation, a short distance from where I watched yesterday and the last few days. My object is to watch the flights of rooks as they pass, and try to settle if each band has a recognised leader or not. Of course it is obvious that no one bird can lead the various bands, for these come from over a large tract of country, whilst even those that seem most to make one general army, fly, often at considerable intervals of time, and quite out of sight of each other.
"A good many are already flying in the accustomed direction, but singly, or wide apart. Each bird seems to be entirely independent.
"The first band now approaches. One rook is much in advance for some distance. He then deviates, and is passed by the greater number of the others, who continue on their way without regard to him.
"Another great, irregular, straggling body in which I can discern no sign whatever of leadership. Then comes another, more compact. A rook that at first leads by a long interval is passed by first one and then another, so that he becomes one of the general body.