The Great Tidal Waves of Bird-Life
TWICE every year a wave of living birds, almost inconceivably grand in the number of birds involved, surges over North America. The autumn wave rolls from the arctic tundras of Canada and Alaska to the torrid valley of the Amazon and the great pampas of the La Plata, only to roll back again to the ice-bound northern ocean with the northward progression of the sun. And almost as ceaseless as the ever-rising, ever-falling swell of the ocean tides is this miraculous tide of beating wings and pulsating little hearts. The last stragglers of the northward migration do not reach their northern home before the early part of June; but in July the southward-setting tide has begun again.
The number of birds that make up this mighty wave almost passes comprehension. Probably more than ninety-five per cent of all birds making their summer home between the northern boundary of Mexico and the Arctic Ocean, that is in the United States and Canada, help to swell the great bird-tide that moves southward in autumn and northward in the spring with the regularity of a pendulum. Allowing a little less than one migratory bird to an acre, we get the enormous number of 4,320,000,000 birds, whose wing-beats follow with rhythmic precision the southward and northward movement of the sun. This number is too vast to be easily comprehended, so let us bring it within our grasp by a few illustrations.
If we allow six inches, the measure of the English sparrow of our streets, to be the average length of a migratory bird, then this mighty host, if we could arrange its restless, fitting members in a quiet, orderly manner, like soldiers on parade, would make a line 4,090,909 miles long. This earth is much too small for such a line. We might arrange our birds in three hundred and twenty-six lines, and each one would extend from the north pole to the south pole along the whole length of North and South America. If we arranged the birds at the Equator, they would circle the globe one hundred and sixty-three times.
Not that every kind of migratory bird travels the whole distance of the wave: no; some swing back and forth through a distance of only a few hundred miles, while others, who make up the extreme margins of the great wave, travel twice a year from the soggy tundras and spruce forests of Alaska to the waving plains of pampas grass in Patagonia, a distance of eight thousand miles.
It will undoubtedly surprise the reader who is not an ornithologist to learn that we do not really know the cause of these great tides of bird-life. One is tempted to say: Why, birds leave the north, because they can get no food during the winter. This statement, although undoubtedly containing the original cause of bird-migrations, is only partly true at the present time; for many birds leave their northern homes at a time when their food is most abundant. The redheaded woodpecker, who in late summer lives largely on grasshoppers and other insects caught on the ground, always leaves the latitude of St. Paul about September 10. It adhered to this date even in the autumn of 1907, when this region had no frost at all before September 27, and when the temperature rose to 96 in the shade as late as the 1,2th, with insect life abundant well into October. Other insect-eaters start southward as early as July 10, when their food is most abundant; and the same is true of many seed-eaters.
Again, if scarcity of food is the cause of migration, why do bluebirds, warblers, thrushes, and waterfowl forsake a land of plenty in the south to rush northward so early that frequently millions of them starve during the cold snaps of our northern spring ? The spring of 1907 furnished a tragic illustration of this. A cold spell accompanied by heavy snows, the latter part of April, fell like a plague upon the migrating flocks. Starved warblers, thrushes, and kinglets were found everywhere. The dead birds found in this latitude belonged to about twenty different kinds, and the number of birds that perished in the Middle West alone must have reached well into the millions. There would have been plenty of room for these birds to breed in the well-provided south; then why do they, year after year, brave storms and starvation in the north ? Many theories have been advanced and numerous treatises have been written on the subject, but for many birds the question remains unanswered.
The problem of the real home of the birds is just as perplexing. If originally the birds were driven southward by advancing winter, then their real home is in the north, where they now breed; if, on the other hand, they originated in the south, and later, for some reason, acquired the habit of seeking more northerly breeding-grounds, then their home is in the south, where they live now during the northern winter.
Many South American birds migrate northward, during March and April, when winter begins in that hemisphere. Some sea birds, like the albatross and the frigate bird, breed on a few uninhabited islands in mid-ocean, and roam over the sea throughout the warm and temperate regions of the globe the rest of the year. Not one of our northern wanderers breeds in its genial winter home in South and Central America. When their time arrives, they all hasten back to the distant north, to build their nests and raise their young in the same region where their own cradles swung from northern trees and bushes.
One might think that South and Central American plains and forests would ring with the music of our warblers, thrushes, and bobolinks, while we are anxiously watching the fall of the mercury and the rise of coal prices; but this assumption would prove false; our northern songsters are silent in the tropics. Perhaps they rest their voices and recuperate from the strenuous season of bird-opera, as human tenors and prima donnas do in mountain taverns and seaside villas.
If a man were to tell the birds which way to travel in their flight from stormswayed pines to the palms and lianes of the tropics, he would bid them direct their course by way of Florida, the Bahamas, Cuba, Hayti, Porto Rico, and the Lesser Antilles.
“ On this route,” he might say to the winged millions, “ you are always in sight of land. If a storm threatens, you can rest until the sky is clear again, and none will be drowned in the raging waves in a vain effort to beat up against the storm on feeble wings.” This advice sounds well and the route looks good on the map, but not a single bird follows this way as his regular route.
“ If this route does not please you,” the bird-adviser might continue, “ there is another that is almost as easy. Go from Florida to Cuba and thence to Yucatan.”
So natural does this route look that years ago American ornithologists practically took it for granted that the migrating hosts followed it, until actual field observations showed that it is as deserted as the one first mentioned. Only a few adventurous or storm-driven birds use the two routes which the bird-adviser would recommend. The most probable reason why they are not used is that they could not furnish sufficient food for the millions of North American migrants. This is especially true of the Lesser Antilles, whose total area is about equal to that of Rhode Island.
Without human assistance, the birds have selected several much-traveled highways between North America and Central and South America. By far the greater number of the birds of the Atlantic coast follow a route from northwestern Florida to Southern Mexico and Central America, making a seven-hundred-mile flight across the Gulf. In spite of this long sea-flight and its many dangers, this is decidedly the popular route with the birds of eastern North America. While the two easy island-to-island routes are deserted, this Florida and Gulf route is literally alive with large and small birds for eight months of the year. Night after night the winged myriads steer northward in spring and southward again in the autumn. Over a vast expanse of sea they find their way, where for ten or twelve hours at a time they are entirely out of sight of land. But in spite of all dangers and difficulties this is the popular route with North American birds.
About ten species reach South America by way of Florida, Cuba, and Jamaica. This list of travelers includes vireos, cuckoos, wood thrushes, tanagers, bank swallows, night-hawks, and bobolinks. But so immensely in the majority are the bobolinks that bird men have referred to this route as the Bobolink Route. It involves only a five-hundred-mile flight from Jamaica to South America, but it is not a generally popular route.
The favorite route for many birds of the Mississippi valley also extends across the broad expanse of the Gulf, directly southward from the mouth of the Mississippi.
The migrants making their summer home on the Great Plains and in the Rocky Mountain country seem to be favored by nature, as they reach their winter homes in Mexico and Central America by short and easy overland journeys. Many birds of California per form what is known as a vertical migration. They journey to the warm lowlands and coastal plains to spend the winter, and in spring return to their summer homes on the slopes and in the valleys of the mountains.
The great southward-moving wave does not come fully to rest until December, or even January. At this time, when food is scarce in the far north, several birds of the Canadian zone become at least occasional temporary sojourners in the northern United States. It is the large snowy owl, the tame evening grosbeak, and the beautiful and trusty crossbills, that come, so to speak, with the last ripples of the ebbing tide.
But, wonderful as is this great migration of birds, the journeys of each species are almost as marvelous, and each kind of bird presents a problem in itself.
The golden plover and the bobolink are known to almost everybody, either from nature or from books and descriptions. Let us try to follow the journeys of only these two birds.
The golden plover is one of the greatest and boldest wayfarers of all bird-dom. Late in April or early in May I find them in this latitude in the Mississippi valley. Toward the middle of the month they have all disappeared, and I do not see them again until the next year. Where are they the rest of the year ? It is now known that their summer home lies far beyond the Arctic Circle, while they spend the winter two thousand miles south of the Equator. Early in June they reach their breeding grounds in the barren coast tundras of the Arctic Ocean, which extend from Hudson Bay to Behring Sea. Many of them travel even much farther north, and have been found nesting on the arctic islands as far as a thousand miles north of the continent, in latitude 81°. Less than two months suffices for them to raise their young under the midnight sun, among the lichens and mosses of the tundras, below which the soil never thaws out. In August the tundras are again deserted, and the ringing cries of the plovers now enliven the bleak rocks and coast of Labrador. Here they feast on the fruit of the crowberry, a low creeping vine which covers hundreds of square miles. A few weeks of such feasting make them fat and strong. Gradually they move southward to Nova Scotia, from where they strike boldly out to sea, flying directly southward toward the coral-strewn beaches of the tropics. If the weather is favorable, they make the whole journey from Nova Scotia to the mainland of South America, a distance of twenty-four hundred miles, without touching land. Sometimes they make a short stop at the Bermuda Islands, but many times they have been seen five hundred miles east of the Bermudas in mid-Atlantic. Some flocks linger for a few weeks on the Antilles and on the north coast of South America, but in September they all reach southern Brazil and Argentina, the great plains country of the La Plata. Here they remain six months, from September to March, enjoying a long vacation after six months of hazardous travel and absorbing family cares.
Early in March they disappear from the La Plata country, but the great majority of them, at least, do not return north the way they came. Very soon they appear in Guatemala, then in Texas. By the end of April they have traveled up the Mississippi valley to the latitude of Minnesota. About the first of May they cross into Canada, and by the first of June they are once more excavating their nests, and preparing to lay their chocolate-spotted eggs, a thousand miles beyond the circle of the midnight sun.
What a wonderful journey it is! How the performance of the most persistent globe-trotter fades into insignificance when compared with the annual journeys of the plover, a bird not larger than a robin. The human traveler has at his command all the science and the technical skill which the human race has accumulated since the first man timidly trusted himself to a dugout wooden boat. The plover’s brain is not larger than a hazel-nut, but in this tiny magazine is stored away, as individual experience or race-instinct, all the intelligence needed to steer the bird over sea and land, over mountains, forests, and deserts, through raging storms and black fogs. Twice a year the plovers make a trip of eight thousand miles north and south, while their northward route lies three thousand miles west of their southward route. Each year of his life a plover travels from twenty to twenty-two thousand miles, and this record he keeps up until his little heart ceases to beat.
Another and most remarkable journey is that made by the bobolink. This wellknown songster of meadows makes his summer home all through the eastern states, as far north as New Brunswick and Nova Scotia, and westward to Montana and Manitoba. One would naturally think that the northwestern bobolinks would leave the United States by way of Mexico or the Mississippi Valley, but, so far as is known, not a single bobolink takes that route. Instead, all the bobolinks of North America migrate via the rice-fields of the Carolinas, and leave the United States by way of Florida, After the breeding season the males doff their clownish-looking dress of black, white, and buff, and assume the plain, brownish garb of the females. At the same time the birds assemble in flocks and start southward.
After the 1st of September all have left their breeding-grounds, and September 9 is the latest I ever saw bobolinks in the latitude of southern Minnesota. Finally, all the bobolinks of the country gather in countless thousands in the ricefields of the Carolinas, where they are known and feared as rice-birds or reedbirds ; and every year the rice-growers of the South have to expend tens of thousands of dollars to protect their crops from being literally eaten up by the bobolinks. Robert of Lincoln, minstrel, clown, and general entertainer of our northern meadows, appears to the Southern ricegrower as a veritable pest. Fifty years ago the bobolinks gathered the fuel for their long sea-voyage from the wild rice of the marshes; since then they have discovered that the cultivated rice makes a better food and fuel, and every autumn they levy a heavy tax on the rice-growers of the South Atlantic states.
After they have grown fat on rice, they leave for Cuba. From Cuba their route leads over Jamaica, but many of them have gathered such a surplus of fat and energy that they make the seven-hundredmile flight to South America without stopping in Jamaica. Arrived on the mainland, they travel as far south as the valley of the Amazon and southern Brazil, where they spend the winter.
About the first of May the northern nature-lover takes an early morning ramble through fields and meadows, and there is the bobolink, swinging and singing from brier and reed, in full nuptial plumage. He has traveled from four to six thousand miles since you saw him last, and has escaped thousands of shotguns and numerous other dangers. Every year of his life he performs this journey, until his bubbling voice has grown silent, and his little quivering body has come to rest in some lone marsh or among the grass of the pampas.
Every one who is somewhat familiar with the structure and the habits of wild swans, geese, and ducks is not surprised to learn that these large water-fowls can annually perform long journeys. Their bodies are powerful engines, adapted equally well to a rushing flight through the air and to a restful locomotion on the water. Moreover, in autumn their plumage is so thick and dense that it is not only perfectly water-proof and frostproof, but almost shot-proof.
But how can we express our wonder and admiration when we learn that such feeble and tiny folk as the warblers and humming-birds undertake voyages as great as, or even greater than, the swift teal and the majestic swan ? The blackpoll warbler, a bird smaller than the chickadee, makes its summer home as far north as Alaska, and winters in Brazil, traveling from ten to fifteen thousand miles a year.
The rufous humming-bird, a wee bit of a bird, scarcely larger than a bumble bee, makes its summer home and builds its tiny nest on the spruce of Alaska, and spends the winter among the flowers of tropical Mexico. Twice a year it journeys up and down the Pacific coast, a distance of three thousand miles.
The warblers are not strong flyers, and their loose, fluffy feathers are a poor protection against storm, rain, and cold. During the summer months about sixty different kinds of warblers enliven the woods of North America clear up to the treeless north and to the cold treeless ridges of the mountains, but during the winter scarcely a single warbler remains in the United States. Nearly all of them are great travelers and make their winter home in Mexico, in Central and South America, and in the West Indies. Very often fogs and storms confuse and bewilder them on their journeys, thousands dash themselves to death against the light-houses along the coast, and tens of thousands are swallowed up by the waves of the storm-lashed Gulf. But in spite of all these dangers they will not stay among the palms, where food is abundant and where no great danger threatens them. An uncontrollable longing that defies all danger and hardship impels them onward to their far boreal homes as soon as the new leaves are budding on the northern willows and poplars.
There is a popular opinion that birds follow closely the advance of warmer weather northward, but close study has shown this idea to be wrong. With very few exceptions, the birds travel northward much faster than the warmth of spring, and are constantly overtaking colder weather. The pretty yellow warblers leave the latitude of New Orleans under a temperature of 65° F., and they arrive on their breeding grounds at Great Slave Lake under a temperature of only 47° F. They travel over a distance of twenty-five hundred miles in twentyfive days, but spring requires thirty-five days to travel from New Orleans to Great Slave Lake.
The higher the latitude the birds reach, the faster they travel. The little blackpoll warblers average about thirty miles a day from New Orleans to southern Minnesota. Then they begin to increase their speed like race-horses on the home stretch, and when they approach their northernmost breeding-grounds in Alaska they average about two hundred miles a day.
Most of our common song-birds migrate by night, flying in clear weather at a height of a mile or more above the earth. This explains why it so often happens that one finds no birds in the afternoon, while early next morning the earth is all alive with them, as if they had dropped out of the sky over night. In this case appearances are not deceptive. They have actually dropped from the region of the clouds.
How do birds find their way ? There is no doubt that they are often guided by sight along coasts, lakes, rivers, and valleys, which are plainly visible for a great distance from the height at which birds travel. In other cases, old birds which have been over the route lead the way, and the young birds follow their calls and their leadership. What wonderful stories these winged travelers could tell, if they could only talk to us; what fascinating teachers of geography they would make for our children! It has, however, been shown lately beyond reasonable doubt that, in addition to keen sight, acute hearing, individual experience, and race instinct, birds possess what must seem to us a kind of sixth sense, the sense of orientation. The Harriman Alaska Expedition found flocks of murres, a sea-bird, flying straight for their home on a lonely rock island thirty miles away, through a fog so thick that everything a hundred yards away was absolutely hidden from view. What human brain could guide a ship thirty miles through a dense fog without a compass ?
Still more conclusive demonstration of this sense of direction in birds has recently been furnished by Professor John B. Watson. He caught and marked fifteen sooty terns and noddies on the Dry Tortugas in the Gulf of Mexico and took them out to sea. Some of the birds were carried as far as Cape Hatteras, eight hundred and fifty miles north of the Tortugas, before they were set free. The sooty terns and the noddies are southern birds which seldom range farther north than the southern coast of Florida; and it is not likely that any of those experimented on had ever been farther north; but none the less thirteen birds out of fifteen found their way back to the Tortuga Islands.
Since the days when Aristotle wrote his quaint accounts of birds and beasts, science has made much real progress, and many of Aristotle’s wonderful stories have been found to be fables; on the other hand, science has added many more real marvels to natural history than it has destroyed of fictitious ones. Aristotle tells us that swallows and other birds hibernate. No real bird-student believes that story nowadays; but it is a remarkable coincidence that even to-day no man knows where one of our most common swallows, the little bank swallow or sand martin, spends the winter — a bird so common that almost every country boy has peeped and poked into its holes in the sand-banks. It disappears somewhere in the great interior of South America, that is all we know.
Another bird-mystery is furnished by the chimney swift, or chimney swallow, as it is popularly called. In August great flocks of them are found everywhere east of the Rocky Mountains. In Minnesota and North Dakota I have frequently met flocks, numbering from one thousand to five thousand, roosting in the chimneys of schoolhouses and churches or other large buildings. Early in September they leave this latitude. Gradually, millions of them reach the Gulf coast, and then they disappear until March. If a great aerial tidal wave had carried them to the moon, their disappearance would not be any more complete. They must winter somewhere in Central or South America, but no ornithologist has yet found them there. It seems almost incredible that a bird so well-known, and whose individuals must be counted in millions, should thus far have eluded all observers, but it is nevertheless true.
Science will soon lift the veil from many of the mysteries of the great bird-tides, but as one mystery disappears, another and a greater one will appear; and as our knowledge grows, our wonder will grow still more.