Richmond Mayo-Smith, Thomas Allan Ingram and Hans Friedrich Gadow

“ Emigration affords a natural outlet for the superfluous labour force of a country. The supply of labour is somewhat reduced, but wages are kept up for those who remain. Those who go find means of bettering their own condition beyond the seas, where they become producers of food and raw material for the home country, and at the same time customers for her manufactured products. Emigration is therefore an economic gain, both directly and indirectly. ”

“ It has been argued with some show of reason that the real home of a bird is that country in which it was born, in other words where the species breeds, but this is not in every case a valid conclusion. It applies to most creatures, but it can well bear exceptions if we leave sentiment aside. When it comes to a question of domicile, the ten weeks’ sojourn of the swift, Cypselus, in England are more than weighted down by the nine months or more which these birds spend in southern countries, although we do not know whether they are resident there or roam about. ”

“ Although emigration does not diminish population, yet, as the emigrants are in the most productive period of life (15 to 45) , the country of emigration loses adults and replaces them with children. It thereby loses the cost of rearing that number of people to adult age, and is left with a disproportionate number of children and old people. The age distribution of the population of Ireland lends some support to this view. In the same vein it is urged that voluntary emigration takes away the cream of the working-classes. ”

“ Under external migration are comprised emigration and immigration, denoting simply direction from and to. The emigrants are at the same time the immigrants; that is, the material of the movement is the same, but the effect upon the country giving up and the country receiving the migrant requires separate treatment. Hence it is proper to separate emigration from immigration. Temporary migration, or travel for purposes of business, enterprise or pleasure, will be considered only incidentally, and because in some cases it is difficult to distinguish between such movements and permanent migration. ”

“ The species which resort to Britain and to other temperate countries in winter are simply those which have their breeding quarters much nearer the poles, and in returning to them on the approach of spring are but doing exactly as do those species which, having their winter abode nearer the equator, come to us with the spring. The birds-of-passage proper, like our winter visitants, have their breeding quarters nearer the pole, but like our summer visitants, they seek their winter abode nearer the equator, and thus perform a somewhat larger migration. ”

“ The mode in which the want of sustenance produces migration may best be illustrated by confining ourselves to the unquestionably migrant birds of our own northern hemisphere. As food grows scarce towards the end of summer in the most northern limits of the range of a species, the individuals affected thereby seek it elsewhere. Thus doing, they press upon the haunt of other individuals: these in like manner upon that of yet others, and so on, until the movement which began in the far north is communicated to the individuals occupying the extreme southern range of the species at that season ”

“ It has been ascertained by repeated observation that in the spring-movement of most species of the northern hemisphere the cock-birds are always in the van of the advancing army, and that they appear some days, or perhaps weeks, before the hens. It is not difficult to imagine that, in the course of a journey prolonged throughout some 50° or 60° of latitude, the stronger individuals should outstrip the weaker by a very perceptible distance, and it can hardly be doubted that in most species the males are stronger, as they are bigger than the females. ”

“ It is the man of energy, of some means, of ambition, who takes the chances of success in the new country, leaving the poor, the indolent, the weak and crippled at home. It is maintained that such emigration institutes a process of selection which is unfavourable to the home country. ”

“ All we seem to know is that not a few kinds manage, in various parts of the world, to cross enormous distances without the chance of a break. It was Gaetke’s notion that migration was for the most part carried on at such a height in the air as to be beyond our ken, and that what comes to our perception consists chiefly of the abortive or unsuccessful attempts, when birds are checked in their course, and being unable to proceed present themselves to our sight and hearing. ”

“ The breeding time is the busiest period of a bird’s life; then the numbers of each species are suddenly multiplied, and so is the stress of providing food, and the particular food which is best for the young may not be available in every country. The idea that the arctic circle is the original home of the numerous kinds of birds which breed in it, whence they are now periodically driven away by stress, has been coupled with the glacial epoch, that supposed solution of so many difficulties. ”

“ Internal Migration.—In modern times there is constant movement of population within national lines, from section to section, and especially from rural districts to the cities. No record is kept of this, and we can trace it only through the census statistics of birthplace. In the United States, for instance, it was shown in 1890 that more than 21·5 per cent. of the native-born inhabitants were living in a state other than that in which they were born. Still further, it appears that about one-half of the native-born inhabitants had moved out of the county in which they were born. ”

“ Cities grow more rapidly now than formerly, because the excess of deaths over births has been turned into an excess of births over deaths. Thereby the cities are becoming less dependent upon immigration for increase of population than formerly, but the migration still goes on. The causes of migration from country to city are mainly economic. In early stages of culture men are scattered over the country, or at most gathered together in hamlets and villages. ”

“ Although several generations may elapse without a migration, it is believed that the locusts when they migrate do so in the direction taken by predecessors. They are said to take trial flights to ascertain the direction of a favourable wind, and that they alight and wait for a change. The most obscure point is their disappearance from a spot they have invaded. A swarm will alight on a locality, deposit there a number of eggs, and then move on. But after a lapse of a season or two there will be few or none of the species present in the spot invaded. ”

“ The process of migration, in its most striking cases, is now very complicated. Many a bird goes actually to the arctic regions for the shortest of summers, but spends most of the year within the tropics. On the other hand there are many species which do not go so far north, but stop to breed in the intermediate regions. We must not take the extremes when trying to unravel the development of the problem. The periodical migrations of mammals, with their more limited extent and greater leisure, are less perplexing. ”

“ In England the song-thrushes receive in the autumn a considerable accession in numbers from the birds which arrive from the north, though the migration is by no means so well marked as it is on the continent, where the arrival of the strangers sets all the fowlers at work. In most localities in Britain the newcomers depart after a short sojourn, and are accompanied by so many of the homebred birds that in some parts of the island it may be safely declared that not a single song-thrush can be found from the end of November to the end of January, while in others examples can always be seen. ”

“ The inhabitants of the country immediately surrounding a town of rapid growth flock into it; the gaps thus left in the rural population are filled up by migrants from more remote districts, until the attractive force of one of the rapidly-growing cities makes its influence felt, step by step, to the most remote corner of the land. Migrants enumerated in a certain centre of absorption will consequently grow less with the distance, proportionately to the native population which furnishes them. ”

“ In Germany the towns of 10,000 and over show a much more rapid increase than the rural districts; and the same fact is generally true of the other countries of Europe. This more rapid increase of population in cities is due only in part to migration from the country. Until the 19th century deaths generally exceeded births in cities, so that if it had not been for constant immigration the cities would not only not have grown, but would have decreased in population. ”

“ It will probably be found that every gradation still exists in various parts of the world, from a complete coincidence to a complete separation of the breeding and the subsistence areas; and when the natural history of a sufficient number of species is thoroughly worked out we may find every link between species which never leave a restricted area in which they breed and live the whole year round, to those other cases in which the two areas are absolutely separated. ”

“ This meant the opening up of the world to commerce and the extension of European civilization to vast areas formerly peopled by savages or half-civilized peoples. It meant a great outlet for the spirit of enterprise and adventure, relief from over-population, an enormous increase in wealth and power, and a struggle for supremacy among the nations of Europe. Colonization and colonial policy excited immense attention in Europe ”

“ Birds breeding in the tropics are always resident, except when they breed on mountains, where the climate causes them to descend into the valleys for the winter.”
In many countries we find that while there are some species, such as in England the swallow or the fieldfare, of which every individual disappears at one period of the year or another, there are other species, such as the pied-wagtail or the woodcock, of which only the majority of individuals vanish—a few being always present—and these species form the so-called “partial migrants.” ”

“ For instance, when the common toad, which is a strictly terrestrial creature, wanders every spring to a frequently distant pool in order to spawn there, this is a true migration. The same applies, strictly speaking, to those insects which hibernate in the ground, at the root of the tree on which they feed and breed. The grey plover breeds in the arctic circle and winters in equatorial countries. To complicate matters further, it is not necessary that the migration be undertaken periodically, more than once, by the same individual. ”

“ Emigrants who have been successful in business return in order to end their days in the old country. Those who have not succeeded return in order to be cared for by friends and relatives, or simply from home-sickness. Thus, for Great Britain and Ireland, while the emigration of persons of British and Irish origin was, in 1905, 262,077, the immigration of persons of the same category was 122,712, leaving a net emigration of only 139,365. In the United States’ statistics we cannot distinguish in the outgoing passenger movement emigrants from other persons. ”

“ The birds, not the individuals, but the species, are supposed to have inherited such a loving reminiscence of their old home, that after thousands of years—with most of the small birds meaning as many generations—they returned at the first opportunity. ”

“ As a matter of fact, emigration has not succeeded in diminishing the population of Europe, which, on the contrary, doubled during the 19th century. The one great exception is Ireland, where population declined from 8,175,124 in 1841 to 4,458,745 in 1901. From 1851 to 1901 the total emigration from Ireland was 3,881,246 or 72·5% of the average population. Emigration, by carrying off the young men and women, also reduced the Irish marriage and birth-rates, which were almost the lowest in Europe. ”

“ But, though we know almost nothing of the migration of birds of the other hemisphere, yet, when we regard the comparative deficiency of land in southern latitudes all round the world, it is obvious that the feathered population of such as nowadays exists can exert but little influence, and its effects may be practically disregarded. ”

“ Whether they have come from far or from near we know not, but other birds certainly come from a great distance, and yet make their appearance with scarcely less exactness. Nor is the regularity with which certain species disappear much inferior; every observer knows how abundant the swift (Cypselus apus) is up to the time of its leaving its summer-home—in most parts of England, the first days of August—and how rarely it is seen after that time is past. ”

“ Doubtless immigration in the last fifty years of the 19th century had a modifying effect on American life; but on the whole the power of a modern civilized community working through individual freedom to assimilate elements not differing from it too radically has been displayed to a remarkable degree. ”

“ We may admit that inherited but unconscious experience, which is really all that can be meant by instinct, is a factor in the whole matter—certainly, as Wallace seems to have proved, in originating the migratory impulse, but yet every aspect of the question is fraught with difficulty.
Less than nothing is known about the speed at which birds fly during their long stretches of migration. ”

“ Further, some of the larger birds, for instance swans and cranes, are still immature in their second year, and yet they migrate like their older relations. It seems permissible to use this fact as an indication that the breeding as such is not the prime reason of their wanderings. The fundamental impelling agent must have been the want of food, and what we usually understand by migration cannot suddenly have sprung into existence to its full extent, but is more likely the cumulative effect of the doings of countless generations. ”