T. A. Coward

“ The solution of the problem is in the interest of science, and therefore of intellectual progress, teaching us the great part which migratory birds play in the scheme of nature. The millions of birds which wander, season after season, from one zone to another, represent an enormous aggregate of labour, by flight and search for food, acting on "the organic life of nature as does the regulator of a steam-engine, at one time accelerating, at another retarding." ”

“ But putting aside economic and utilitarian considerations, there is to some of us a greater stimulus to solve the problems of nature. With the birds, [130] and the insects and plants upon which they feed, we share a common heritage, and the more we learn of the life of these, our fellow workers, the nearer we approach solution of the great riddle of the Universe, the mysterious law-abiding scheme of Nature. The book of knowledge to which we may add some iota is marred with mystery, superstition and error, but each proved fact cleanses its pages. ”

“ Early fall migrants, and indeed the majority of autumn migrants all the world over, travel more slowly than in spring; they are neither impelled by sex-impulses nor the need to escape from failing food supplies. A little later the supply does slacken and with it the temperature cools, and if the changes are sudden southward migration is accelerated. Migration, however, is such an advantageous and well-established habit that it usually begins before hurry is necessary, and the birds loiter southward, feeding as they go. ”

“ As the northern spring approaches, the strongest of all animal instincts, on which reproduction and the very existence of the species depend, overcomes all other desires, and the bird grows restless. The hereditary instinct, the origin of which we have endeavoured to show, urges the bird to seek the breeding area which has by degrees become so far removed from the winter quarters. ”

“ Before the winter resident golden plovers have arrived in autumn and after they have departed in spring, the favourite fields are regularly visited by passing flocks, and the lower reaches of the Mersey, where the common sandpiper is rare as a summer resident, are visited every autumn by parties of birds on passage. Chance may lead a casual wanderer to a good food-supplying spot, but the regularity of appearance suggests habit and memory. ”

“ Some take for granted that the Polar Regions were the original home, the centre of dispersal, of all northern birds, and consequently that migration originated in the gradual pushing back of avian life as the ice gained more and more land each year. During the summer, the birds, urged by an irresistible love of home, travelled as far north as the ice allowed them, but gradually they were driven to nest further and further south until they found refuge in the unglaciated parts of the earth. ”

“ Possibly in the early days of migration only the mature birds did return; that we cannot state one way or the other. But it is reasonable to argue that once a regular migration habit has become not only confirmed by heredity but a very true advantage to the species, its influence will be felt by each and every individual. Again it is clear that the sexual impulses, in an undeveloped form, are appreciated by the adolescent, and in many animals by even the most juvenile. ”

“ That there is an overruling relation between the advance of spring and the passage to northern breeding quarters, and the gradual cooling in autumn and the retreat to winter quarters is, of course, evident, but it must not be held, as contended by the early students of migration, that this is the sole factor which regulates migration. The actual relationship between the weather and the movement of birds is far more complicated than one would imagine, and the stimuli of continental or overland travelling differ from those of a cross-sea flight. ”

“ Migration is the act of changing an abode or resting place, the wandering or movement from one place to another, but technically the word is applied to the passage or movement of birds, fishes, insects and a few mammals between the localities inhabited at different periods of the year. The wandering of a nomadic tribe of men is migration; the mollusc, wandering from feeding ground to feeding ground in the bed of the ocean, migrates ”

“ The play of all young animals is either an imitation or reflection of the search for food—the hunting instinct—or the love-making and sexual quarrels pertaining to reproduction, the pretended competition by the young for the favours of the opposite sex. ”

“ Mr Eagle Clarke says that the importance of winds is overstated, but as an incentive only. The direction of the wind has no influence as an incentive but its force is an important factor; in a strong wind a bird may be blown out of its course. Birds will not start in a high wind but may pass into the influence of strong winds which may affect both progress and direction. He adds that particular winds usually prevail during the season of great autumn movements, which are not incentives but are the result of pressure distribution which is favourable to migration. ”

“ From what little we do know about the behaviour of our summer birds in their winter home, we may safely conclude that their habits are similar to those of winter visitors to Britain. Only in a few species are there two restricted areas, two abiding places or homes. The necessity of retaining a secure home for the young and the care of these young during their more helpless age keeps the individual birds within a certain area during the breeding season, but at all other times the bird is more or less of a wanderer. ”

“ The natural answer, the cravings of nature and sexual impulses fails to give satisfaction in every case. Wanderings in search of food might lead in any direction, and probably did in the first place, but now birds in the main travel south in search of food and north in search of home, and many of them perform immense journeys, passing over or through lands which are capable of supporting a wealth of bird-life even in the winter months. ”

“ It has been suggested that some of the sexually mature non-breeders may be actually enjoying their winter during our summer; in other words that they have bred in southern breeding-stations whilst their congeners wintered in the same zone. This means a double breeding-area for certain species—a possible explanation, but one hardly supported by known facts. When a bird had so cosmopolitan a range that in the course of its dispersal its breeding areas were separated, we almost invariably find that the birds inhabiting these two areas are distinguishable geographical forms or sub-species. ”

“ They visit fields top-dressed with manure, glean the refuse of the harvest, frequent the farm-yards, and in early spring, visit the budding larches to prey upon their insect pests. On the other hand golden plovers and lapwings are remarkably local in their winter habits, and so long as the weather remains open will frequent the same fields throughout the winter. ”

“ And even in most favourable weather birds fall exhausted. During a stay on the Yorkshire coast in autumn, when migration was even-flowing and unchecked by adverse weather, I found several goldcrests which had reached land only to die, and though most birds came in without showing signs of fatigue, a few larks and starlings were so tired that they made little effort to escape when approached. ”

“ Many have insisted that wherever migrants cross the sea they do so along submerged coast-lines or over submerged land-bridges, arguing that the gradual evolution which has made the advantageous adoption of a habit of migration possible was unable to eliminate the hereditary tendency to follow the exact route by which their ancestors passed from place to place. ”

“ The discovery of masses of torpid swallows, dead or dying, by no means an unknown thing when birds are overtaken by sudden falls in temperature in autumn or by a severe setback in the spring, was to these puzzled men confirmation of their theory of hibernation. ”

“ I have seen bands trailing south in autumn in which all the birds were immature, and others in which a number of young were accompanied by a few mature birds, though, certainly, these old birds did not appear to lead. Another assertion, that the old and young do not even travel by the same route rather supports the idea that the young birds find their way simply by a sense of direction, a sense liable to blunder, whilst the old birds travel [61] by the perfected or best route which their experience has taught them. ”

“ Only to a certain extent can it be safely contended that the present route of a species is an indication of its earlier journeys, or that the direction of original dispersal is recapitulated in the present line of migration. Heredity, experience, and imitation would certainly tend to preserve and confirm the general direction; the shortest and easiest passage from food-base to food-base would become an hereditary route, unless circumstances arose which caused a change. ”

“ So, inexperienced young birds, travelling instinctively by orientation may, and do, make mistakes.
Human beings, in varying degree, possess a sense of direction, and some a wonderful power of finding their way in strange places; it is most marked amongst those men we choose to call uncivilised, who, indeed, live in closer touch with nature than those of us who depend so much on compass, map, road, train and tram ”

“ We know it breeds farther north than our wheatear, but its winter range is not fully worked out. The smaller bird is found in north and north-western Africa, and the larger form farther east, even south of the equator on the eastern seaboard, and probably, when we know more about the range of the two we shall find that the form breeding farther north, winters farther south.
The folly of laying down the law on the strength of the knowledge of the habits of a few species is shown by the study of the movements of American birds. ”

“ In the evolution of some routes land-bridges certainty appear to have played their part, but once those bridges have ceased to influence direction the shortening of the time occupied by the lengthening of the single oversea flight is only a question of generations when an advantage to a species is to be gained. ”

“ The oft-repeated assertion that birds can foretell the nature of approaching weather—that they are living barometers—is not supported by any satisfactory evidence, but it is certain that on many occasions the weather into which they have passed in moving from one zone to another has not only retarded, checked, or exhausted them, but has proved fatally disastrous. ”

“ But the lengthening of the journey might surely be occasioned in another way, and the evolution of migration assisted apart from any [31] glacial influences. Each successive increase of the length of the journey taken by the stronger and more go-ahead individuals, leading them in advance of the bulk of southward moving and competing birds, would be a distinct advantage to the individual and consequently to the species. The pioneer would arrive, like the slower movers, in a land already peopled with an avian population, but it would not have its own fellows to add to the stress of competition ”

“ Each theory, though it may apparently explain certain phases of migration, can be answered by some exceptional difficulty which makes it fail as a full explanation; we are driven to the conclusion that birds possess a sense of direction, which is often, very incorrectly, called Orientation. ”

“ Birds of Passage or Spring and Autumn Migrants: birds which neither nest with us nor normally remain for the winter, but merely use the British Islands as feeding and resting places on their journey between the northern breeding area and the southern or eastern winter quarters. This group is an especially difficult one, for in it must be included such birds as dunlins and curlews, which are represented as breeding species in Britain, and also a number of birds which apparently go no further south than our islands in winter, and others which, though not breeding, go no further north in summer. ”

“ I doubt if birds always intentionally make use of strong winds, currents which would carry them for great distances at a considerable speed, but the preliminary ascent may be to search for these currents. Cyclonic and anticyclonic winds, even when at an altitude of some thousands of feet, would carry them easily, and probably it is the wind-borne individuals, parties, or even hosts, which drop for a refuge to the first island they see when carried far from their migratory path. They are carried rather than drifted from their pathway, borne in the moving current whether they wish it or not. ”

“ The arguments against it are that not a single instance of avian hibernation will stand the light of reason and investigation, and that birds are provided with the means of escaping from the cold zone and certainly use these means. There are flightless birds, but they all live in climates in which they can exist at all seasons. As Seebohm puts it—"The hibernation of birds is a theory, the evidence in support of which has completely broken down. The migration of birds is a fact, as completely authenticated as the fact of their existence." ”

“ The individuals and the species, if not the whole families of birds, which failed to retreat, went the way of the "thousand types." On the retreat of the ice, the birds, impelled by a mysterious hereditary memory of home and of the good times enjoyed by their remote ancestors, for very very many generations must have been born under more or less sedentary conditions during the Ice Age, began the same pushing forward each year to the limits allowed them. ”

“ They may play at and actually perform a migration [28] which is so closely bound up with the life of the species. That this impulse has not always sufficient strength to force them to perform the whole journey is apparent from the fact that many non-breeders, young or sexually mature, on their northward journey through our islands or along our coasts, never reach the breeding area; the food supply on the way attracts them more than the memory of home; they linger with us until the breeding season is over and the return journey has begun. ”

“ The swallow supports Seebohm's thesis that the individuals which go farthest to the south in winter, breed farthest north. A day-migrant and by no means a rapid one, the swallow may be timed from place to place, and it is not presumption to suggest that the birds which reach Britain to nest came from lands little south of the Sahara and well north of [67] the Equator, and that those which pass through England and along our shores in May and even June are on their way from Southern Africa to the northernmost limits of their range. ”