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IV

THE BIRDS’ AIR LINE

BEFORE we knew as much about the earth as we do now, the complete disappearance of many birds in the fall and winter was considered a great mystery. With us one day, they were gone the next. Then, months later, they suddenly reappeared. Where had they been?

At one time it was thought that some birds flew to the moon. Others, particularly the Swallows and Swifts, were believed to fly into the mud and pass the winter hibernating like frogs; while the European Cuckoo was said, in the fall, to turn into a Hawk.

Why birds were ever thought to winter in the moon it is difficult to say; but that Swallows were considered to take refuge in the mud at this season is not so surprising. We have seen how these birds sleep in the reeds in the marshes.

Anyone finding them in bed, as it were, before they were fully awake in the morning, might be pardoned for thinking that they had just come out of the ground and were perched in the reeds waiting for their feathers to dry.

The belief that in the fall the European Cuckoo turned into the Sparrow-hawk of the same country is doubtless to be explained by the fact that the Cuckoo leaves for the south in the summer; while the Hawk, which it resembles in color, stays throughout the winter.

Now that we have explored nearly every corner of the earth, there are only a few birds whose “routes of migration,” as they are called, are unknown. We have learned that these routes are followed just as regularly as though, like our highways and railroads, they could be seen.

The birds’ air line, as we shall see, is not always the shortest distance between two points. It was not made in a day, or by one surveyor. Many, many years have passed since the first bird trav­elers on any one of the many air lines followed by birds began their spring and fall journeys; and what was a good direction at one time may not have been at another.

HIGHWAYS AND HABIT

It seems to be a law among bird travelers that every bird must follow the route over which its parents flew. This the ornithologist calls “inherited habit.” It is just as though children born in Arizona whose ancestors had emigrated across the continent from New York City should go to New York City over the route made by their father, grandfather, and great-grandfather, and perhaps great-great-grandfather.

The first part of this route over which their great-great-grandfather traveled may have led to what was then the western border of civilization at Pittsburgh. Then their great-grand­father, like a true pioneer, pushed onward to St. Louis. Here their grandfather was born, and when he became a man he emigrated to the great wheat-growing region of Dakota. In Dakota their father was born and when he grew up he moved to the copper mines of southern Arizona.

Perhaps these children may themselves emigrate to the forests of Oregon. Then what a zigzag journey they would make to New York if like birds they should be guided only by “inherited habit”!

Here comes in the difference between reason and instinct. Instinct would send our children from Oregon to Arizona, from Arizona to Da­kota, from Dakota to Missouri, and finally through Pittsburgh to New York City.

Reason directs them to buy a ticket over the most direct railway line between Oregon and New York City, and they thus make their journey in the shortest possible time.

Let us see how many, many miles the Cliff Swallows of Nova Scotia might save if they were to buy a ticket over what we may call the short, Reason Route, instead of the long, Instinct Way.

THE CLIFF SWALLOW’S ROUTE

The Cliff Swallow winters in South America and in summer is found over most of the United States, except Florida, and north to the Arctic regions. If we look at a map we will see that Nova Scotia is directly north of Colombia in northern South America. The Cliff Swallows pass through Colombia on their northern jour­ney. We might, therefore, expect them to follow one of the most traveled of birds’ air lines. This leads across the Caribbean Sea and Gulf of Mexico and up the Atlantic coast through New England to their summer homes. But instead of going by this, the most direct way, they go westward through Panama, then northwest through Central America and Mexico. It is not until they reach Texas that they fly directly toward the place they desire to reach. They cross the United States by going up the Missis­sippi and Ohio Valleys, and avoid the south­eastern states entirely.

Why is it that they thus travel two thousand miles more than is necessary? We can only be­lieve that they are following the route made by their ancestors. The Cliff Swallow is a bird of the West. There it builds its singular, bottle shaped mud nest under overhanging cliffs and ledges. But in the East, where it is much less common, it places its close-set rows of mud tene­ments beneath the eaves of barns and other outbuildings. So it is probable that Cliff Swallows, or, as they are also called, Eave Swallows, have come from the West to the East in recent times. In migrating, therefore, they go back over the old Instinct Way, or over the trail of their ancestors.

Long, roundabout journeys like this are the exception. I have spoken of them because they seem to explain better than more direct air lines how these wonderful highways, thousands of miles in length, may grow, little by little, from small beginnings.

MAIN TRAVELED ROADS

Now let us trace some of the more popular routes. If we were studying the travels of European as well as of American birds we should learn some of the most interesting facts. For instance, we should find that in flying from Europe to Africa birds cross the Mediterranean Sea at a point where the water is so shallow that it is believed the two continents were formerly connected there. The land bridge which, it is thought, formerly guided the birds in their flight has disappeared, but the habit of crossing at this particular place still remains.

Though I do not know of any cases of this kind in America, we shall find equally interest­ing facts concerning the air lines of our birds. For example, how do you suppose the little Wheatear, no larger than a Bluebird, formed the habit of migrating from Africa to Green­land? Probably he comes by way of England and Iceland, but at the best it is a long journey and seems to take the bird much farther than it is necessary to go. In the fall he goes back to winter in Africa.

Doubtless some European waterbirds visit us every year, but the Wheatear, so far as I know, is the only land bird which migrates regularly between North America and Africa. With this exception no North American land birds leave the Western Hemisphere in their migrations. Their motto might be “See America first!” Cer­tainly many of them see a large part of it.

The birds of the western United States are not such great travelers as those of the eastern part of our country. Some of them only travel from the higher parts of the Rocky Mountains or Sierras, where they nest, to the low, warm valleys in which they winter.

Those that leave the United States go into Mexico. Some continue their journey as far south as Guatemala, but few go farther. They all travel overland, and do not therefore en­counter the dangers to which many of our east­ern migrants are exposed.

It is surprising that most of the bird travelers of Alaska migrate to the eastern United States. Some of them actually go to their winter homes by way of Florida and the West Indies! But when we examine a map we find that a large part of Alaska is east of the Rocky Mountain system. These mountains, like a great wall, have prevented the western birds from crossing to their eastern side; while the bird pioneers from the East have found nothing to prevent them from taking up fresh claims until they reached this same great wall in the far Northwest. So far as birds are concerned, therefore, Alaska is like a small United States. The birds that live west of the mountains, on what is called the Pacific slope, travel southward with other west­ern birds. Those found east of the mountains travel southeastward and then join in the journeys of eastern birds.

This is the route the little Blackpoll Warbler follows in his seven-thousand-mile journey from Alaska to northern South America. There is no question about the straightness of his air line! He lays his course directly across Cuba to Jamaica and from Jamaica to Colombia in north­ern South America. That is a journey anyone might be proud of. What a marvel it is that it should be made regularly twice each year by a creature only five and a half inches lang!

In their travels across the United States, birds seem to follow coast lines and river valleys. They must pass through a country which will supply them with food when they pause to rest. Even if they fly over us we cannot expect them to stop if we can offer them nothing to eat.

Near my home at Englewood, New Jersey, is a small ice pond. Sometimes the dam which makes it is raised and the water runs out. This happened once in August, a season when many shore birds are migrating. When the pond was full I had seen none of these birds. But the very day that the pond became a field of mud, large numbers of Sandpipers of several species stopped to feast on the little aquatic animals which had been left stranded. So we cannot always tell what kind of birds may be traveling far over­head in the sky, unless we have some way of making them stop and call on us.

When we follow some of the more famous bird travelers in their journeys we shall become familiar with the routes they travel. Now we shall outline the routes of only those migrants which leave the eastern United States in the winter.

One route leads southward and southwestward into Texas and Mexico, Central and South America. Another does not enter Texas and Mexico at all, northwestern Florida being used as the port from which many birds embark on their seven-thousand-mile journey across the Gulf of Mexico to Yucatan, whence Central America is followed to South America.

A third route, which we have seen is used by the Blackpoll, passes from Florida to Cuba and thence to Jamaica and over the Caribbean Sea to South America. A fourth leads from Florida to the Bahamas. A fifth, which is one of the most remarkable of any, crosses the Atlantic Coast from Nova Scotia to South America.

Some birds spend the entire winter at sea. Indeed they may never put foot on land except when they visit it to nest. Frequently in going by steamer to Florida or Cuba I have seen thou­sands of those little web-footed Snipe, the Red and the Northern Phalaropes. They were from fifty to one hundred miles off shore, riding the great waves like corks. Here they live from August until May, feeding on small forms of sea-life and sleeping in the “cradle of the deep.” With them were many Loons. We think of these weird-voiced birds as solitary dwellers on woodland lakes, but off the coast of Virginia I have seen as many as 5,000 in a day.

The swallow-like Petrels which, during the summer, so often follow vessels in the North Atlantic, nest in February and March in certain islands in the Antarctic Ocean. When their young are reared they all travel northward to spend what is really their winter off our coasts. Unless storms should blow them ashore, they probably never touch land from the time they leave their home in the Far South until they return to it.

SUGGESTIONS FOR STUDY

What bird travelers have you seen in their winter homes? When did they arrive? Where had they come from? How long did they stay? Do you know where any of our summer resident birds that come to us from the south in the spring spend the winter? Trace on the map a route from New York City to Oregon by way of Pittsburgh, St. Louis, South Dakota, Arizona, and Oregon. About how much longer is it than a direct line from Oregon to New York City? Trace on the map the route followed by a Cliff Swallow that winters in South America and nests in Nova Scotia. What European bird travels every year to eastern North America ? Where do many of the migrating birds of the west­ern United States spend the winter? Follow on the map the migration route of the Blackpoll Warbler. Trace on the map some of the principal migration routes of bird travelers of eastern North America. Mention some birds that spend the winter at sea.

Have you ever seen a Stormy Petrel? What is the origin of the name Petrel? Where do many of the Petrels nest that we see on the Atlantic Ocean during the summer? How does their “time-table” differ from that of a bird which nests in North America and winters in the Tropics?