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XI

THE BIRDS’ COMPASS

HAVE you ever been in a small boat off­shore in a fog? It is not a pleasant experience. You venture out, perhaps to fish or sail, on some fine, clear day, when suddenly a bank of fog comes creeping in from the sea. Almost before you see it, softly, silently, swiftly, it surrounds you. The shore becomes dim and soon disappears. Probably you have no com­pass, and unless a fog siren, the wind, or the tide gives you a clew, you may soon be quite at a loss to say where the land lies.

Then you will be fortunate if somewhere near by there is a nesting colony of sea birds. In the Gulf of St. Lawrence, where I have had such an experience as I am describing, there may be Murres, Auks, or Puffins. Off the coast of Maine we would find Herring Gulls. If we were near Nantucket we might expect to see the Terns that nest on Muskeget Island.

If some of these birds also had gone out to fish at sea, when the fog came what would happen to them? The deep, bellowing roar of the siren could mean nothing to them. I doubt if they would notice the direction of either wind or tide. Nevertheless, bird after bird would go swiftly through the fog, returning to its home just as directly and surely as though it could be seen distinctly. Then if we were wise, like many fishermen before us, we would set our course by the birds and reach land in safety. So the birds would then be our compass. But what compass do they steer by?

Some years ago, when nearing the end of a voyage across the Atlantic, I discovered a Cur­lew aboard the steamer. The season (it was in May) and the fact that several Wheatears had also just taken passage with us showed that we had entered one of the birds’ highways of migra­tion.

The Wheatear is a small bird about the size of a Bluebird. It is one of the few birds which regularly travel from Europe to eastern North America. The first Wheatears reach England from the South about March 1, but at that time they certainly could not continue their journey to Greenland and Labrador. Possibly, there­fore, the early corners settle in England. If this is true, it is probable that the later birds are the ones which cross the Atlantic to nest in North America. Perhaps the very birds which had boarded our steamer were making this wonder­ful journey.

They seemed so small and weak when seen flying above the ocean over which they had em­barked so bravely, that one could not believe their tiny wings were strong enough to battle with its storms. Then as one thought of the length of their journey over the trackless waters, it seemed even more remarkable that they should be able to steer a course which would bring them safely to the land for which they had started.

How do they do it? What is the secret of the power which guides them on journeys where man, without the aid of chart and compass, sex­tant and chronometer, would surely lose his way?

If the Curlew did not give me an answer to this question, he had at least given me an exhibi­tion of the confidence with which birds set out on voyages from which man, unaided, would shrink. The Wheatears, when I walked too near them, flew to some other part of the steamer. Evidently they welcomed a lift on their long flight. But the Curlew, as I attempted to photo­graph him at short range, without the slightest hesitation left his perch on one of the steamer’s boats and flew out to sea. He did not swing around to the stern to follow us but flew on ahead. There was no wavering in his course. With as much certainty as the man at the wheel pointed the steamer’s bow toward the Irish coast, so did he point his bill toward land. He seemed to know where he was going. His speed was much greater than ours and soon he was lost to sight.

At this time Fastnet Light, the nearest land, was distant one hundred and forty miles. From the height at which the Curlew was flying, the horizon was distant not more than six miles. Even if his eyes were like telescopes he could not, therefore, have seen the coast. But if it had been so near that the beaches and marshes where he might find his favorite fare were in plain sight, he could not have started for them more directly. Small use had he for the steamer! Doubtless before we arrived he had found a hearty meal.

“Seeing is believing,” says the old proverb, and this Curlew, boldly, confidently striking out ahead of us with all our equipment for following the proper route, seemed to prove that he was possessed of some special power which held him to the proper course.

But if it was surprising to see a bird start on a voyage of one hundred and forty miles, what would we think if we should see the Turnstones begin their two-thousand-mile journey from Alaska to the Hawaiian Islands? Or what should we say of a Golden Plover as he began his two-thousand-four-hundred-mile flight from Nova Scotia to South America? Or how shall we express our amazement that tiny Warblers, Vireos, and Flycatchers can wing their way through the blackness of the night and after traveling thousands of miles arrive on the date on which they were due?

So we repeat the question which people for years have asked before us—how do they find the way? Or, in other words, what is the birds’ compass? Sight may be of assistance to birds on short journeys, but, as we have seen, it would be of small service over hundreds, not to say thou­sands, of miles of water. The sense of smell is poorly developed in birds, but in any case it would be of no value over the distances they travel. Their sense of hearing is very acute. When they are migrating they frequently utter their call-notes. Doubtless these serve to keep birds of the same kind together. But the leaders of a flock or company hear no calls ahead to guide them.

Taste and touch have certainly nothing to do with it. So we conclude that birds possess a sixth sense. This has been called the sense of direc­tion. The sense of sight we know exists in the eye, and the sense of hearing in the ear, and in the nerves leading from these organs to the brain. But no one knows where the sense of direction is situated. Indeed, it is only within the last few years that naturalists have ventured to speak of a sense of direction as something which actually exists.

Sometimes this sense is designated as the “homing instinct.” So we speak of the homing instinct of Carrier or Homing Pigeons. But the homing instinct and the sense of direction are really two different things. The first impels the bird to start; the second guides it on its way. Everyone knows in a general way that when Carrier Pigeons are taken from their homes and released, they at once start on the homeward journey.

But, generally speaking, Pigeons are at first taken for only a short distance, and they gradually learn to make long flights only after they have made shorter ones. The owner of the Pigeons usually does not care to risk losing his birds by taking them so far from home that they may never return. But it is also true that the first homing flights of Pigeons are often over routes which they have never seen before. The journey may be short, but like the sea birds in the fog, they would not know what direction to take if something did not tell them, and this some­thing is the homing instinct or sense of direction.

Before the discovery of wireless telegraphy, Captain Reynaud of France was forming a Pigeon post service for the French Army. Among his experiments he released Pigeons from steamers when they were out of sight of land. I still have a message which he sent me from the steamer on which he was returning from this country to France. Surely something more than sight was required to bring the bird that bore this message back to its home in New York City. It has been suggested that from the cage in which they were confined the Pigeons might see the country through which they were passing. They could then, some people have supposed, remember the main landmarks and thus find their way back.

But there are not many landmarks at sea, and another experiment by Captain Reynaud clearly proved that Pigeons can return to their homes over a country which they could not possibly have seen. In this experiment he took five Pigeons, when they were under the influence of chloroform, from Orléans to Évreux, France. This is a distance of about seventy miles. After two days, when they had thoroughly recovered from the effects of the drug, they were released, and at once returned to their home in Orléans. These birds, therefore, were certainly not guided by anything that they had learned of the route while traveling to Évreux.

The natives of certain islands in the South Pacific use Frigate or Man-of-War Birds for messengers. Probably this custom is of much older origin than our employment of the Pigeon. The Frigate Bird is a great wanderer. With wings which measure, when spread, about eight feet from tip to tip, its body is not much larger than that of a good-sized chicken. It can there­fore remain in the air for long periods and, if necessary, make great journeys without resting. We cannot prove that the birds used as messengers on the Pacific had not in some manner learned the routes over which the natives sent them. But in the experiments which I am about to relate we know that the birds used had never before made the journey from the place where they were released to the place from which they were taken.

These experiments were planned by Professor Watson of Johns Hopkins University. The birds used were Sooty and Noddy Terns. Many thousands of these birds nest on Bird Key, a tiny islet in the Dry Tortugas. In order that he might study their habits Professor Watson lived alone on the Key with them for three months.

Birds which know nothing of man generally have little or no fear of him, so Professor Watson was soon on friendly terms with the Terns of this remote island. He could go among them and cause no more alarm than one would in walking through a poultry yard. This tameness permitted him to learn many interesting things about their home lives. He also made a number of tests to see whether birds which were taken some distance from the Key and released would return to it.

He caught several birds and with aniline dyes stained their feathers various colors in order that he might recognize them. First he took three Noddies. Some were set free only twenty miles, others sixty miles, from the Key. All returned within from one and three-quarters to about three and a half hours after being given their freedom.

Then two Noddies and two Sooties, after being colored, were sent to Havana, a distance of one hundred and eight miles. They were re­leased on the morning of July 11th, and returned to the Key the next day. It may be said that these birds had flown over this route before, but in the next test the birds used were taken on a voyage over a part of the sea about which they could have known nothing.

On June 13th, three Noddy and two Sooty Terns were caught and marked, and sent from Bird Key to Key West. Here they were placed in the hold of a northbound steamer. They were carefully fed and watered, and on June 16th were released about twelve miles east of Cape Hatteras, off the coast of North Carolina. This is about one thousand and eighty miles by water from Bird Key—a long journey even for the most highly trained homing Pigeon. But the birds’ compass pointed the way, and on the morn­ing of June 21st, both the Sooties were found on. their nests, and one of the Noddies was seen several days later.

Still we might say, as someone indeed suggested, that these birds simply followed the coast line until they reached their island home. Though why they should go south instead of north, or turn westward through the Florida Keys instead of eastward to the Bahamas, where many Terns of their kind live, is not explained.

However, to make it perfectly clear that the birds were not guided by landmarks of any kind, Professor Watson finally sent several Sooty and Noddy Terns across the Gulf of Mexico to Galveston. This city is distant eight hundred and fifty-five miles from the Tortugas, and the intervening water is unmarked by islet, shoal, or reef. Nevertheless, one of the birds returned to Bird Key in six, one in seven, and a third in twelve days from the time of release.

It is, therefore, practically certain that the birds used could not have been familiar with the route, nor could there have been other birds of their kind to guide them. From the hold of the vessel they certainly could not have observed the water over which they were sailing, and if they had, it would not have given them a clew to a return route. We can, therefore, explain their remarkable feat only by believing that they were guided by what we call the sense of direction.

No experiments that I know of seem to prove more clearly than these of Professor Watson that birds possess this sense.

Doubtless it is this sense which each year leads fishes to their spawning grounds and seals to their “rookeries.” It appears also to exist to some extent in man, particularly uncivilized man. But man, besides being more intelligent than the animals below him, possesses powers of observation and reason which make him less de­pendent on the promptings of instinct than they are

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SUGGESTIONS FOR STUDY

Do you ever have any difficulty in naming the points of the compass when you are in a strange place ? Have you ever been lost in a fog? Can you find your way about an unfamiliar city easily? Have you ever seen Homing Pigeons flying back to their loft? Do you know anything about the length of the journeys these Pigeons make and the time required to make them? If you have ever seen birds flying through a fog, describe the circumstance. Have you ever had a bird fly aboard your steamer when at sea? What was the nearest land at the time? What was the season of the year? Where do you think the bird had started from and was bound for? Do you think it was on or off its course?

Describe some of the experiments of Professor Watson. Do they indicate the existence of a sense of direction in birds? Do you know of any cases of domestic animals finding their way home? Had they been over the route before? By what sense or senses were they guided?

Define the difference between the “homing instinct” and the “sense of direction.”