MIGRATION

From Agepedia

MIGRATION or ANIMALS. The migration of animals, that is, the travelling of a large number of the same species toward a certain place of destination, or in a certain direction, is one of the most remarkable phenomena in natural history. Migration takes place with quadrupeds, fishes, birds and insects. As to the first, it does not appear that any of them migrate periodically and regularly, like many species of fish and birds, for which a sufficient reason may be found in the almost uninterrupted passage which air and water permit, whilst the land offers many impediments to change of place. Yet some quadrupeds are suddenly seized by the desire of migration. The lemming rat, which is found in the northern parts of Europe, migrates at irregular periods, when a severe winter is approaching, in incredible numbers, and always in a straight line, stopping not for rivers or lakes. Some other quadrupeds, also, occasionally move in large numbers, and for considerable distances ; but these expeditions do not take place at regular periods, and seem to be owing to accidental causes. The buffaloes (properly bisons), in the western wilds of North America, and the wild hurses, sometimes take long journeys in large bodies. Some fishes, also, remove into warmer situations during winter; thus the salmon leaves the rivers and shores, on the approach of winter, to seek the warmer* waters of the deep sea. Other fish do the same. The codfish move, in great numbers, about the month of May, from the northern seas toward Newfoundland. The shoals of herrings, which periodically traverse the ocean, are innumerable. The same is the case with the mackerel, pilchard, anchovy, &c. That insects migrate is well known, for instance, locusts (q. v.), ants (q. v.), &c, and move, with surprising obstinacy, in a given direction. The animals, however, with whose migrations man is most familiar and which appear to migrate most regularly, are some species of birds. The facts which are known relative to this point are very curious, and yet leave a vast field for interesting observation. Some birds regularly return, after a certain absence, not only to the same country, but to the same spot where they built their nests before, or where they were bred. Many storks, which become half tame in Germany, have been marked, and found to return regularly to their old nests, built on a wheel, which the peasants of that country, particularly in the north, place, for that purpose, on the corner of the roofs of their houses. The same is related of swallows, and other birds of passage. Other birds do not return to a particular country, but travel, according to circumstances, from one to anotner. Among the former are some which remain in the country of their nativity only as long as is necessary to breed and bring up their young ; others are absent but for a very short time. The loriot remains but three months in the middle regions of Europe, whilst the lark is absent but for a very short time. Mr. Brehm, a German, has collected many interesting facts respecting the birds of passage. Generally speaking, they are determined as to the place where they build their nests, by the means of subsistence which they find, as, for instance, the grosbeak, goldfinch, pigeons, cranes, landrails, several species of herons, woodcock, geese, ducks. In 1819, the fruit of the pine tree being scarce in the north of Europe, whilst it was very abundant in the central parts, large numbers of the crossbill, which chiefly lives upon this food, were found in the latter regions. The drought, in 1819, made the meadows around Altenburg, in Saxony, very dry, and no landrails (in general frequent there) were seen during that season. They had fled to the valley of the Rhine, where the drought had been less. The cold in the winter, also, has much influence on the migration of birds. The winter of 1821- 1822 was very mild in Middle Europe, whilst, in the north, it was unusually cold, in consequence of which many birds were seen in Germany which hardly ever quit the northern regions. Some birds of Bohemia went to Switzerland, and some birds arrived in France which never had been seen there before. The contrary took place during the following winter, when the mercury stood, in Germany much lower than in Sweden, Hunters, and other people living much in the open air, know that certain birds do not migrate, except on the approach of a severe winter. How are these birds led to migrate at such seasons ? The general and easy answer is, by instinct.' But what is instinct ? Certainly we cannot mean, by this term, a constant direct interposition of Providence, which drives the birds away because a severe winter is coming on. Instinct, whatever it may be, must be guided by general laws. In what way, however, the birds are led to guard against .the severity of the approaching season, whether by a peculiar sensibility to the causes from which its severity will proceed, or in other ways, we know not. In the article Instinct, it has been maintained, that much of the conduct of animals necessarily implies reflection. The vicissitudes of the atmosphere, on the arrival of the migrating time, have also a great influence upon them. Most birds perform their migration during the night; some species, however, by day. Others stop not, either by day or night. To the class which fly by day belong the birds of prey which obtain their food by daythe crow, pie, titmouse, wren, woodpecker, chaffinch, goldfinch, lark, swallow, and some others. Those which travel by night are the owl, blackbird, &c, and a great number of aquatic birds. Those which stop not, day or night are, the heron, wagtail, yellowhammer, plover, stork, crane, wild goose, swan. It is veiy remarkable, that individuals of those species which travel day and night, and which, by some cause, are prevented from migrating, remain, during ail the time of the migration of their species, awake, and only occupy themselves with taking food. These birds like particularly to travel in bright moonlight. Many birds obtain their food on the wing. The swallows, traversing the sea, catch insects, and fishing birds catch fish, whilst they continue their journey. If the titmouse, wren, woodpecker and pie rest, for some time, on the branches of trees, they soon resume their flight, after having fed. Those birds which habitually alight on spots where they find nourishment in abundance, never remain longer than two days in succession, if nothing opposes the continuance of their flight. It is a curious fact, that, at these times, many birds utter cries such as they are never heard to make at any other time. Unless obliged by fogs to keep near the ground, birds generally fly very high during their migration. Of all migrating birds the cranes are, perhaps, the most remarkable. They seem to be most endowed with foresight. They call each other by certain cries, several days before they depart, assemble, and make a great noise, as if consulting, after which they range themselves in two lines, forming an angle, at the vertex of which is the leader, who appears to exercise authority and give orders, for instance, to form a circle in a tempest, or to be watchful if eagles approach, &c. ; he also gives the sign to descend and take food. If he is tired, he places himself at the end of the line, and the bird next behind him takes his place. They utter, during the night, more piercing cries than during the day, and it seems as if orders and answers were given. Wild geese and ducks travel in a similar way. To enable birds to fly with ease, and to continue long on the wing, they must fly against the wind, in which respect flying is directly opposite to sailing. Sportsmen are well acquainted with this fact. If the wind is unfavorable for a time, the migration is retarded, yet never entirely given up, 01 Iy the birds arrive much leaner, fatiguec by their efforts. It is astonishing how tender birds, as the linget, for instance, set out from the extremity of Norway, and brave a long journey even over the ocean. The quails, who are heavy in their flight, wait on the shores of the Mediterranean, often a long time, for a favorable wind, of which they immediately avail themselves, halting on all the islands. If the wind suddenly changes, many are drowned in the sea. Certain birds, as the moorhen, rail, &c, being unable to fly for any considerable distance, travel partly on foot. Some even (as the great auk, or penguin, diver and guillemot) migrate by water. Ornithologists have observed that, on the old continent, birds migrate in autumn to the southwest, and in spring toward the northeast; yet the courses of rivers and chains of mountains exercise considerable influence on the direction of their flight. On the new continent, the points of direction are not the same. Captain Parry has satisfied himself that the birds of Greenland go to the southeast. It is remarkable, also, that the young of certain species do not make the same journey as the old birds ,o they go more to the south, so th?t it is very common to find* in the south of Europe, only the young birds of a certain species, whilst the older ones remain more to the north. In other species, the females go farther south. It was formerly believed that the birds of the tropical regions never migrate, and that they never pass the line; but Humboldt has shown that this is not the case. He observed, moreover, that the migration there took place with the periodical rise ofrivers.