The same characteristic of uncommon numbers holds true of the crows and, indeed, of all other species of birds, save one, that ever practise the wing drill. Wild geese when in small companies, each a family unit, have a regular and beautiful [[114]]flight in harrow-shaped formation; but I have never witnessed anything like a wing drill among them save on one occasion, when a thousand or more of the birds were gathered together for a few days of frolic before beginning the southern migration. Nor have I ever seen the drill among thrushes or warblers or sparrows or terns or seagulls, which sometimes gather in uncounted numbers, but which do not, apparently, have the same motive that leads crows or starlings to unite in a kind of rhythmic air-dance on periodic occasions.
A second marked characteristic of the wing drill is that it is invariably a manifestation of play or sport, and that the individual birds, though they keep the order of the play marvelously well, show in their looks and voices a suppressed emotional excitement. The drill is never seen when birds are migrating or feeding or fleeing from danger, though thousands of them may be together at such a time, but only when they assemble in a spirit of fun or exercise, and their bodily needs are satisfied, and the weather or the barometer is just right, and no enemy is near to trouble them. Whatever their motive or impulse, therefore, it is certainly not universal or even widespread among the birds, since most of them do not practise the drill; nor is it in the least like that mysterious impulse which suddenly sets all the squirrels of a region in [[115]]migration, or calls the lemmings to hurry over plain and forest and mountain till they all drown themselves in the distant sea; for no sooner is the brief drill over than the companies scatter quietly, each to its own place, and the individual birds are again alert, inquisitive, well balanced, precisely as they were before.
The drill is seen at its best among the plover, I think; and, curiously enough, these are the only birds I know that practise it frequently, in small or large numbers and in all weathers. I have often watched a flock come sweeping in to my decoys, gurgling like a thousand fifes with bubbles in them; and never have I met these perfectly drilled birds, which stay with us but a few hours on their rapid journey from the far north to the far south, without renewed wonder at their wildness, their tameness, their incomprehensible ways. That you may visualize our problem before I venture an explanation, here is what you may see if you can forget your gun to observe nature with a deeper interest:
You have risen soon after midnight, called by the storm and the shrilling of passing plover, and long before daylight you are waiting for the birds on the burnt-over plain. Your “stand” is a hole in the earth, hidden by a few berry-bushes; and before you, at right angles with the course of the storm (for plover always wheel to head into the [[116]]wind when they take the ground), are some scores of rudely painted decoys. As the day breaks you see against the east a motion as of wings, and your call rings out wild and clear, to be echoed on the instant. In response to your whistle the distant motion grows wildly fantastic; it begins to whirl and eddy, as if a wisp of fog were rolling swiftly down-wind; only in some mysterious fashion the fog holds together, and in it are curious flickerings. Those are plover, certainly; no other birds have that perfect unity of movement; and now, since they are looking for the source of the call they have just heard, you throw your cap in the air or wave a handkerchief to attract attention. There is an answering flash of white from the under side of their wings as the plover catch your signal and turn all at once to meet it. Here they come, driving in at terrific speed straight at you!
It is better to stop calling now, because the plover will soon see your decoys; and these birds when on the ground make no sound except a low, pulsating whistle of welcome or recall. This is uttered but seldom, and unless you can imitate it, which is not likely, your whistling will do no good. Besides, it could not possibly be heard. Listen to that musical babel, and let your nerves dance to it! In all nature there is nothing to compare for utter wildness with the fluting of incoming plover. [[117]]
On they come, hundreds of quivering lines, which are the thin edges of wings, moving as one to a definite goal. Their keen eyes caught the first wave of your handkerchief in the distance; and now they see their own kind on the ground, as they think, and their babel changes as they begin to talk to them. Suddenly, and so instantaneously that it makes you blink, there is a change of some kind in every quivering pair of wings. At first, in the soft light of dawn, you are sure that the plover are still coming, for you did not see them turn; but the lines grow smaller, dimmer, and you know that every bird in the flock has whirled, as if at command, and is now heading straight away. You put your fingers to your lips and send out the eery plover call again and again; but it goes unheeded in that tumult of better whistling. The quivering lines are now all blurred in one; with a final flicker they disappear below a rise of ground; the birds are gone, and you cease your vain calling. Then, when you are thinking you will never see that flock again, a cloud of wings shoot up from the plain against the horizon; they fall, wheel, rise again in marvelous flight, not as a thousand individuals but as a unit, and the lines grow larger, clearer, as the plover come sweeping back to your decoys once more.
Such is the phenomenon as I witnessed it repeatedly [[118]]on the Nantucket moors, many years ago. The only way I can explain the instantaneous change of flight is by the assumption, no longer strange or untested, that from some alarmed plover on the fringe or at the center of the flock a warning impulse is sent out, and the birds all feel and obey it as one bird. That the warning is a silent one I am convinced, for it seems impossible that any peculiar whistle could be heard or understood in that wild clamor of whistling. Nor is it a satisfactory hypothesis that one bird sees the danger or suspects the quality of the decoys, and all the others copy his swift flight; for in that case there must be succession or delay or straggling in the turning, and the impression left on the eye is not of succession, but of almost perfect unity of movement.
The only other explanation of the plovers’ action is the one commonly found in the bird-books, to which I have already briefly referred, and which we must now examine more narrowly. It assumes that all the birds of a migrating flock are moved not by individual wills, but by a collective impulse or instinct, which affects them all alike at the same instant. In support of this favorite theory we are told to consider the bees, which are said to have no individual motives, and no need for them, since they blindly follow a swarm or hive instinct [[119]]that makes them all precisely alike in their actions. The same swarm instinct appears often in the birds, but less strongly, because they are more highly developed creatures, with more need and therefore more capacity for individual incentive.
This illustration of the hive is offered so confidently and accepted so readily, as if it were an axiom of natural history, that one hesitates to disturb the ancient idol in its wonted seat. Yet one might argue that any living impulse, whether in bees or birds, must proceed from a living source, and, if that be granted, speculate on the absorbing business of a nature or a heaven that should be perpetually interfering in behalf of every earthly flock or swarm or herd by sending the appropriate impulse at precisely the right moment. And when our speculation is at an end, I submit the fact that, when I have broken open a honey-tree in the woods, one bee falls upon the sweets to gorge himself withal, while another from the same swarm falls angrily upon me and dies fighting; which seems to upset the collective-impulse idol completely.
I must confess here that I know very little about bees. They are still a mystery to me, and I would rather keep silence about them until I find one bee that I fancy I understand, or one man who offers something better than a very hazy or mystical [[120]]explanation of a bee’s extraordinary action. Yet I have watched long hours at a hive, have handled a swarm without gloves or mask, and have performed a few experiments—enough to convince me that the collective-impulse theory does not always hold true to fact even among our honey-makers. Indeed, I doubt that it ever holds true, or that there is in nature any such mysterious thing as a swarm or flock or herd impulse.