The Zoologist/3rd series, vol 1 (1877)/Issue 5/On the Migration of Birds

by John Cordeaux

 

ON THE MIGRATION OF BIRDS.

By John Cordeaux.

 

In the last part of the 'Ornithological Miscellany,' under the heading of "Hirundo rustica," Mr. George Dawson Rowley^[1] has propounded an original and startling theory on the migration of birds, a theory which reduces the bird itself to little more than a passive agent, and the act of migration to a great mundane law requiring the exercise of no intelligence or instinct: the so-called migratory impulse being a blind force, like other forces in Nature,—a mere material force impelling the bird forward without any act of will or instinct. To quote Mr. Rowley:—"My idea about finding the way is this; the bird has as much to do with it as a man starting from London to York by the railway. He finds his way, steam conveys him; wind takes the bird. If the steam blows up, the passenger is killed; if the wind changes, the bird dies." Again, "The bird starts on its journey; after it has set forth it is ruled entirely by circumstances of which wind is the chief ... As a ship is ruled by the wind, so is the bird. The bird is a sailing ship, the tail is the rudder, and it is governed by the wind; and this is how it finds its way, just as seeds find their way," i.e., seeds conveyed by ocean currents to distant shores, or from one field to another by the wind.

From Mr. Rowley's theory I am obliged entirely to dissent; for I am satisfied that birds are not guided by the wind. The migratory instinct, or by whatever name we choose to call it, is not a blind force; it is an actual and wonderful intelligence, an instinct hereditary in the bird itself; an instinct called into play by various causes, food, vicissitudes of climate, sexual love; an instinct which has been in force, handed down through countless generations of birds, slowly modified from time to time by such circumstances as a gradual change of climate, or changes in the distribution of land and water,^[2] but still an instinct mighty and all-sufficient for attaining its special object.

Birds are not mere automata, they are something more than this; we are much too apt to consider them from our own peculiar standpoint; we argue about them, their habits and movements, as we do also about other animals, from our own experience. What man cannot very well do with his boasted intelligence, the bird cannot do, forgetting that there is no analogy to be drawn between the two cases. Where we find a race of creatures adapted for long flights, and which have undoubtedly for an enormous period of lime, twice in each year, been accustomed to migrate to and fro across the earth's surface, we may be well satisfied that they must possess in a high degree in their own special organisms the qualifications for the work—qualifications and powers which have altogether been lost or are merely latent in man himself Mr. Rowley says:—"Those who hold the opinion that birds migrate by instinct should read the convincing chapters on the way Indians travel through unknown forests (Wallace's 'Natural Selection,' p. 206, et seq.), which proves that man does not possess instinct, neither can any one find his way in an unknown forest. I contend, then, that what man with intelligence is unable to do, birds must fail to accomplish."

Now I repeat that there is no analogy between the two cases, and that even if it can be shown that man cannot find his way in an unknown region, which I very much doubt, it is really no argument against the bird or other animal not being sufficient for the purpose.^[3] Animals do find their way in some extraordinary manner, by a sort of intuitive instinct, which almost seems like a sixth sense. We have repeatedly, in our own experience, met with remarkable instances in domestic animals—cows taken from their calves, mares and horses from their foals or a favourite pasture, also with dogs taken long distances from home, even by rail—finding their way back again by an entirely new route, and across a perfectly unknown country. One remarkable case I remember of a young horse and mare swimming a great tidal river, or arm of the sea, several miles in width, to get back to their old quarters, which they succeeded in doing. By what power, instinct or intelligence they accomplished this I am unable to say, certainly not on the same principle as seeds are carried by ocean currents, or blown from field to field. Before setting forth on the migratory journey, birds often collect together in large flocks, the species and even the sexes keeping distinct: this shows arrangement, a plan, a special course of procedure—a preparation for the great event shortly to come off. That birds too, under certain circumstances, should delay their flight waiting for a more favourable wind, shows a high degree of intelligence.

An experience of more than twenty years close observation of the habits and manners of birds, more particularly in connection with their annual migrations, has led me to the conclusion that they not only possess far more intelligence than we usually give them credit for, but also know how to make the best use of this intelligence. They do not move in a groove, and are not the mere blind subjects of a great mundane law which Mr. Rowley would seem to infer.

It is a well-established fact that the same birds, both during the vernal and autumnal migration, do return in a great number of instances to the same place. The cases indeed recorded are so numerous that I have difficulty in making a selection. The well-known fact of a Wagtail's nest being built year after year in a particular place, and of a Cuckoo laying her eggs in that nest almost year by year, is one instance. Perhaps, however, the most remarkable case is that mentioned by Mr. Stevenson ('Birds of Norfolk,' vol. ii., p. 55), and previously recorded by Mr. Hewitson ('Eggs of British Birds,' vol. i., p. 209), on the authority of Professor Newton, of a pair of Stone Curlews continuing to resort, year after year, to nest in one particular place (though it was entirely changed in character), long after it, and many acres around it, was planted with trees, and had become the centre of a flourishing wood—namely, the Warren Wood of Elveden, near Thetford, which extends over more than three hundred acres.

In Professor Newton's new edition of Yarrell (p. 565, note), another curious instance is given in the case of several pairs of the Yellow Wagtail (Motacilla Raii) returning year by year to nest in the same haunts, some heathery mounds bordering a stretch of wet meadows on the left bank of the Little Ouse, below Thetford. The whole passage may be commended to the reader's notice.

At the Ashby decoy, Lincolnshire, a particularly marked duck, having a white throat, was known to come in eight winters in succession, and another, a spotted duck, for four or five years. These, and numbers of other cases, which time and space will not permit me to cite, prove most undoubtedly that birds do return year by year to the same spot.

On the east coast of Lincolnshire the arrivals of various species, during the autumn months of September and October, are so regular that they may be readily tabulated and predicted to a few days. The same phenomena may be observed, and with even greater certainty, at Heligoland during the periods of the vernal and autumnal migrations. No matter how the weather is at each particular periods of arrival, calm or strong, thick or clear, the birds come, and come, too, with marvellous regularity. They are scarce or plentiful as the case may be, for the abundance or scarcity of migrants at any special locality is due more or less to the state of the weather during the period of passage. The most favourable circumstances for birds passing the sea are calm still periods, or a light breeze, dead ahead, or a few points free. A head wind that is not too strong is the very thing birds like best, but failing that, a "beam wind," to use a nautical expression, seems to be the best. A wind on their quarter, or one aft—that is, having to fly before the wind, particularly if strong—is objectionable; it ruffles up their feathers and otherwise impedes their flight, soonest tiring them out. The consequences of unfavourable winds are that the birds alight on the first coast they reach for rest: under favourable circumstances they would have passed forward far overhead and unseen. Just as a man, fatigued by an arduous or difficult journey, pauses to rest on the way, so the birds alight for rest and quiet; within twenty-four hours, however, they are off again, each to its especial goal in forest, field, marsh, or sea-coast—a goal which it was their steady, predetermined, purpose to reach when they first took wing from the lone tundra, or ice-girdled shore, in the faraway north. They trusted to no aerial currents to guide or drift them passively towards the sunny south, as seeds in the wash of the equatorial currents to the Hebridean shore, but to their own instinct and intelligence—an instinct which thus far has never failed. According, however, to Mr. Rowley, birds have neither impulse nor instinct: they are purposeless creatures with no will of their own, and the sport of every puff of wind. To carry out, then, this theory we must undoubtedly assign to the winds a far greater constancy than they are usually supposed to have, or than anemometers will justify us in supposing them to possess. The hypothesis is as wild as the wind itself. Nothing, indeed, is more variable than the wind—nothing more variable than the wind during the vernal and autumnal equinoxes, when birds must migrate—blowing, as it does, from every point of the compass in twenty-four hours. Were the birds' movements mainly dependent on air-currents, and air-currents only, we should rarely—although Mr. Rowley assumes the contrary—have year by year the same phenomena occurring at any given locality on our east coast. The arrival or non-arrival of immigrants being dependent on one of the most variable of causes, the results would also be variable, whereas the contrary is the case.

Wind, I am convinced, except in some very abnormal instances,^[4] as great gales and storms, has little to do with the normal phenomena of migration. All animals and man himself undoubtedly prefer favourable weather for travelling; but although they may delay, they do not put off their travels altogether because wind and weather are unpropitious.

Continuing his subject, Mr. Rowley says there is one thing in common between the migration of the seed and the bird—"once started they do not come back till the journey is finished." Does Mr. Rowley seriously wish it to be inferred that any comparison can be drawn between the two phenomena—the one thing an inert mass, the play of wind and current; the other a living, highly endowed organism. The seed returns not by the same path because it cannot, the bird because it will not. Birds are occasionally, however, known to turn back in their migratory journey when they find they have made a mistake. Several instances are on record of migrants during the autumn being seen away off the mouth of the Channel and over the Atlantic, apparently migrating in the wrong direction: they are probably such as on dark foggy morning have overshot the mark, and at daylight discovering their error, are making their way to the nearest land.

There is also the case mentioned by Mr. Stevenson ('Birds of Norfolk,' vol. i., p. 413 et seq.) of the Red-legged Partridges in Norfolk migrating out to sea and again returning. Had the birds in these instances migrated on Mr. Rowley's theory, and not by their own instinct, they ought to have kept going in a direct line without coming back. In fact, on Mr. Rowley's hypothesis, we do not quite see why the bird, once in full migratory swing, should stop again till in the natural course of events it flies itself to death. Compared with the drifting seed, it is positively at a disadvantage, having no sea coast to bring it up: like that marvellous mechanical leg we read of somewhere, which when once wound up and started could not be stopped again, so the bird ought to keep going—aimlessly and purposely, perhaps—but still going.

It is a well-ascertained fact that the young of the year of many birds migrate before their parents, and in separate flocks; these have never travelled the route before, and how they find their way over these thousands of miles of sea and land seems a very puzzling problem. It is a curious fact that although the young come in separate flocks, we constantly find an old bird or two—usually old females—amongst them, so that the young may to some extent be in leading strings. As most birds, however, travel by night, and on very dark ones too, they cannot trust to guidance alone, and they are not able to make use of such landmarks as prominent capes and headlands. They come much as did the old sea rovers,—without chart or compass, "by rule of thumb,"—certain to hit the land somewhere, and when once the land is seen knowing all will be right. With the wonderful vision birds possess, and the great height at which they usually travel, they would be able, much more readily than we suppose, at early dawn to distinguish known features of land or sea coast (supposing them to have travelled the route before) at, to us, immense distances. Nor would their inherited instinct, I believe, fail under any circumstances, whether in young or old, to bring them to their goal.

As a familiar instance of this inherited instinct in birds we may cite the case of the Common Partridge. How is it, except by this, that Partridges, having had no actual experience for many generations of the real Kite or Buzzard, cower or rush at once to the nearest shelter when the paper kite's "shadow saileth across the open shaw"? Some years since, when the telegraph-wires were first carried across the Lincolnshire marshes. Partridges and Plover were constantly' picked up killed by flying against the wires; now, after the lapse of some years, this is rarely if ever the case, the generations of Partridges that witnessed this immolation of their comrades has long passed away, yet the present birds have learnt through this same hereditary instinct to avoid the danger.

Instinct is one thing, the migratory impulse another: we must also take into account, when considering the migration of birds, except the very young, the wonderful powers of memory displayed by animals. Those who are accustomed to ride and drive much, must have noticed how rarely a horse forgets any road he has once travelled, or any house he has stopped at, it may be years previously. Out of many instances, I will mention one of this memory in birds. In 'The Zoologist' for 1875, p. 4698, Mr. Nicholls, writing from South Devon, mentions the case of a young Herring Gull taken from the nest in May, 1871, and brought up in a state of domestication. In May, 1872, it left its quarters, and was given up as entirely lost, but, strange to say, in November, 1873, it returned, then in beautiful plumage, and allowed its old friend and playfellow, a little boy of eight years old, to take the same familiarities with it as formerly.

The migratory seasons are undoubtedly the most important periods in the life of a bird: without these regularly recurring periods life would be impossible for them; their existence and the continuation of their race is dependent on these annually recurring voyages through the air. If, then, the instinct has been so strongly and rapidly developed in birds in the case of the paper kite and telegraph-wires, how much stronger may we suppose it to be in guiding the bird along its air-path towards that bourne which countless generations of its kind have sought before.

Enough I think has been said to prove the untenabilily of this new automaton hypothesis. Indeed, the more it is considered the more absurd does it appear. Nothing short of a miracle would be required to cause a gust of wind to take the same Stone Curlew, in the case above cited (and it is impossible it could have been otherwise than the same bird), year after year, from its winter quarters somewhere in Africa and set it down in its former nesting haunt in what is now the middle of a Suffolk wood.

 

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1. See: Ornithological Miscellany vol. 2 (1877), p. 79 (Wikisource-ed.)
2. Before the enclosure and drainage of the Lincolnshire Fens enormous flocks of various wild-fowl visited the east coast every autumn in incredible numbers. At these times we are told a flock of wild ducks was observed passing along from the N. and N.E. into the East Fen in a continuous stream for eight hours together. Since the drainage and reclamation of the Fen lands the wild fowl have practically deserted our coast, the great migratory stream now passing down the opposite coast of Holland, our principal supply of wild fowl coming from that country. In the shallow waters of the Zuyder Zee, during the autumn migration, the sea is sometimes black for many miles with various ducks. Last year, during the first week of November, immense flocks of swan, geese, and ducks passed Heligoland.
3. Mr. Rowley, I think, has not comprehended Mr. Wallace's remarks, to which he refers in the above passage, so far indeed as I can form an opinion. What Mr. Wallace says of the so-called "instinct" of Indians and other savages in finding their way is that it is the effect of continued observation (aided by inheritance of the faculty) carried on so as to be quite unconsciously exercised. This is really very like the "instinct" of migratory birds.
4. See 'The Field,' March 11th and 18th, 1876, "On some Abnormal Migrations of Birds."