The curlew′s wings beat with a strong, rapid, unchanging rhythm hour after hour. The strokes were deep, smooth and effortless, the wings sweeping low beneath his belly at every downstroke and lifting high over the back with each return. Each stroke was an intricate series of gracefully coordinated actions merged with split-second precision into a single, smooth movement, for the curlew′s wing was a wing and propeller combined. Each portion of the wing had a different flight role to play.
The sturdy inner half next to the body deflected the air-stream as an aircraft wing does, so that pressure developed against the undersurface and suction above—the lift that produces flight. It accomplished this with its aerodynamic shape alone. The flapping of the wings provided forward drive, but was not directly responsible for keeping the bird airborne.
The outer half of the curlew′s wing, composed of the ten stiff flight feathers overlapping like a Venetian blind, was the propeller that drove the bird forward, producing the airflow that gave lift to the inner wing. The wing bones were along the leading edge of the wing, and most of the wing behind them consisted of flexible feathers. Hence on the downstroke the pressure of air twisted the wing, bony front edge down and trailing feather edge up, which turned it into a propeller blade pushing air backward and driving the bird ahead. The wingtip flight feathers were additional small propellers, for each central quill was also nearer the front than the rear, so that air pressure twisted each one individually, the same way the whole wing twisted, pushing air backward and adding forward drive. With the upstroke, the air pressure bent the wing and feathers the opposite way, now front edges up and rear edges down, so that the push of feathers against the air still produced a forward propulsion, and the lift force of the inner wing remained uninterrupted with no loss of altitude on the upstroke.
It was all reflexive, automatic, too rapid for conscious control. The curlew completed three or four wingbeats a second to give him a flight speed of fifty miles an hour.
Occasionally one of the curlew′s wings would bite into the harder, spiraling air of a vortex left by the wingtips of a migrating shorebird ahead of him, for even the passage of another bird left a trail in the air that the curlew′s delicately sensitized wings could detect. Usually this alteration in the air pattern was the curlew′s first warning that he was overtaking a flock of birds ahead. When he found one of these vortexes, the curlew took advantage of it and followed it in with one wing riding the updraft edge of the horizontal column of spiraling air. In this way he found a degree of lift ready-made for him and his own wings could work a little easier.
But no other shorebird except the golden plover flew as fast as the curlew did, and each time he slowly overtook the bird producing the vortex ahead. First he would hear the faint twitter of a flock′s flight notes, the vortex would grow stronger, then the birds would appear as blurred figures against the grey sky in front. The curlew would fly with them for a time, but his greater speed would gradually drive him ahead. Then once more he would be flying alone.
This happened several times during the night, for the air layers close to the cooling tundra were turbulent and most of the shorebirds were flying at the same level just above the turbulence. Toward morning the curlew encountered another vortex trail and adjusted his wingbeat to the change in lift. He followed it for a long time and the vortex remained firm but grew no stronger. This time the curlew wasn′t overtaking the flock ahead. Ducks and geese were not yet migrating, only two birds could be flying out of the arctic now at a speed that the Eskimo curlew wouldn′t rapidly overhaul. They had to be either golden plover or his own species, Eskimo curlew.
The curlew′s tireless wings beat faster and the airflow pressed hard against his streamlined body. The wingtip vortex eddying back from the unseen flyers ahead strengthened, and it was a firmer, rougher vortex than any the curlew had encountered earlier in the night. It grew stronger almost imperceptibly, and the curlew′s eagerness grew with it. A tenuous hope, part instinctive reaction and part a shadowy form of reasoning, formed nebulously in the curlew′s brain. Was this the end of his lifelong quest for companions of his own kind? The curlew′s wingbeat speeded until the powerful sinews of his breast muscles, gram for gram among the strongest of animal tissue on earth, pained with the strain.
The other birds were very close before their figures emerged, faintly at first and then more sharply, out of the darkness ahead. For a minute or more the curlew could detect only the vague, wavering lines of the flock′s formation, then slowly the dark lines separated into individual birds. Only the fast, strong flyers like geese, curlew and golden plover flew in single-column, diagonally trailing lines or Vs that permitted each bird to benefit from a wingtip vortex of the bird ahead yet escape the air turbulence directly behind it. And the curlew knew that the geese flocks were not yet migrating south. A restive excitement seized him and the curlew pushed on harder.
The gap closed rapidly and the birds ahead assumed sharper form. They were small, much smaller than the curlew, yet now there was not the instinctive rejection that had caused him to ignore the Hudsonian curlews and other shorebird flocks. The urge to join a flock was still as pressing as before. The curlew called out softly. Golden plovers answered.
It was a large group of forty or fifty, and the curlew moved in to a rearguard spot at the trailing end of one of the arms of the flock. He slackened flight speed and announced his presence with a rapid, twittering series of notes. The plovers answered again, the whole flock chattering sharply in unison. The curlew′s flocking urge was satisfied. There was a vague, remote feeling of loneliness deep within him still, but the curlew was no longer alone.
Of the thirty-odd shorebirds that fly south out of the Canadian arctic every fall, only the golden plover is suited as a migration companion for the Eskimo curlew. Their flight speeds and food preferences are similar, but there is another more important reason. With their tireless endurance as flyers, the golden plover and Eskimo curlew spurn the easy land route down the continent that all other migrating birds follow. Instead they work eastward to the rocky coasts of Labrador, Newfoundland or Nova Scotia, then strike out straight south over the Atlantic for a gruelling, nonstop flight of twenty-five hundred or more miles that doesn′t bring them to land again until they reach the northern shores of South America forty-eight hours later. Often a big Hudsonian godwit or, occasionally, a shorebird of some other species will join a golden plover flock and follow the plovers down the Atlantic on this long oversea shortcut south. But only the Eskimo curlew and golden plover do it regularly every fall, for only they, of all the arctic′s strong-winged shorebirds and waterfowl, possess the speed and power of flight to breast or escape the midocean storms often encountered. The route enables them to take advantage of the rich crowberry crop that purples the hillsides and plateaus of the Labrador peninsula each fall, a luxuriant store of food missed by the hosts of midcontinental migrants. But in spring the plovers and curlew must follow the usual migratory route up the western plains. For then the crowberries are dead and hard beneath snows of the Labrador winter that linger for weeks after the midcontinent′s arctic is greening with spring.
Toward dawn the grey monotony of tundra, dimly visible far below, began to be pierced by slender, twisting fingers of black. The birds had covered four hundred miles since nightfall and were approaching the tree line where tundra gave way to the matted subarctic forests of spruce. The black fingers reaching into the tundra were forested river valleys where stunted spruce thickets found shelter in the hollows against winter blizzards and precariously survived. With the first yellow-grey flush of dawn the flock dropped to a lakeshore mudflat, rested briefly, then as daylight came they began busily feeding.
The curlew with his stiltlike legs and long, downcurved bill stood out strikingly among the smaller, dark-plumaged, short-billed plovers. But the two birds, competitors and enemies on the nesting grounds, had migrated in company for countless generations and they mingled now as one species. Other shorebirds—yellowlegs, knots and the little semipal-mated and least sandpipers—scurried close in their feeding, then withdrew. The curlew studied them closely, for somewhere in this vast arctic tundra were birds he would recognize as his own kindred.
They fed all day with only occasional breaks for resting. With the darkness they flew again. The flock clung together loosely as they climbed for height, then as they leveled off the birds formed smoothly into a straggling V formation that permitted the inner wing of each bird to gain support from the whirling air produced by the outer wing of the bird ahead. The curlew took the lead position at the point of the V and the plovers fell in behind with a grace and ease as though the maneuver had been long practiced. No conscious selection of flock leader had taken place. The bird at the point position had to work harder to create lift and forward speed out of the unbroken air barrier ahead of it, and the curlew was the strongest flyer, so the remainder of the flock formed automatically behind in a movement as involuntary and spontaneous as each bird′s breathing.
Soon after starting, the black fingers below merged into a solid mat. They were over spruce forest now and the tundra was behind. Other shorebirds were flying straight south toward the western plains, but the curlew led his flock southeastward, veering toward the matted crowberry vines of Labrador. Occasionally the curlew dropped back to an easier flight spot in the body of the flock, but each time after a brief rest he moved forward to the lead again.