« AnkstesnisTęsti »
sentative of their kind had been previously observed for many months. Cranes, storks, some herons, swans, geese, and other large wading birds and water-fowl, often, perhaps usually, fly at a great height and make long passages without alighting, but there is little if any evidence that the smaller land-birds make their journeys at great elevations; but, on the other hand, much to the contrary. During autumn our woods for many weeks are filled with busy troops of mingled species, consisting mainly of vireos and warblers, the general trend of whose leisurely movements is southward, while in spring the movement of similar gatherings is northward.
Whether birds migrate by definite routes, as some writers have maintained, is still a matter for investigation. That such is the case seems probable from their greater numbers near large water-courses than over the country at large, as well as their special abundance at particular points. Their routes, however, evidently vary in different years, as is indicated by the scarcity of some species over a wide area where they are at other times numerous. It is also noteworthy that the vernal and autumnal routes are not always the same, being, it is believed, in a few species habitually different. Birds during migration are also more or less at the mercy of the elements. Heavy storms often deflect their courses, and many thousands sometimes perish by being irresistibly borne far out to sea.
The keenness of sight in birds being duly recognized, together with the fact of the low flight and the short stages by which the passage between distant points, in the case of a large proportion of the species, is usually made, it seems impossible to avoid the conclusion that they are guided largely by the prominent landmarks of the country traversed, as the outlines of coasts, the trend of mountain-chains and of the larger rivers; and that the contrary view, often urged, is based on an erroneous conception of the general facts involved. To this aid must, of course, be added that of memory, both individual and inherited. Evidence that birds direct their course by the sight of well-remembered landmarks seems to be afforded by the state of bewilderment they sometimes exhibit in thick weather, and the mistaken directions they at such times are known to take. The light-houses along coasts, than which there are no more destructive agents of bird-life, are well known to be fatal in proportion to the density of
the fog or the darkness, and the height of the light above the sea. In the thick darkness they become the only objects discernible, and, through strange infatuation, lead the birds only to destruction.
A few birds make long passages over the sea, as in reaching distant islands, or in passing from one continent to another. Ordinarily, the birds of North America which visit Central and South America during the winter migration, make the passage mainly by the way of the West Indies, and thus without being at any time far from land. Many of the migratory birds of Europe pass the winter in Africa, and are thus obliged twice yearly to cross the Mediterranean; but here again no great breadth of sea is encountered. It is otherwise, however, with species that habitually visit distant islands, as the Bermudas and the various groups in the Pacific and Indian oceans. With few exceptions, the birds which take these exceptional and remarkable flights are various species of plovers and sandpipers, the most roving of all birds, many of whom pass from high northern latitudes to quite remote parts of the southern hemisphere. They are, however, evidently not wholly without means of directing their course. Their general experience undoubtedly gives them a sense of direction, so that when not disturbed by unusual exigencies,-as protracted storms and heavy gales,-their ability to find their way is not really so marvelous as at first sight seems. They are strong of wing and can make the passage quickly. The sun may be their guide by day, and the usual phenomena of air and sky, the prevailing winds, and the changes of temperature attending change of latitude, may further aid them in their course. Such flights, considered in all their bearings, are, perhaps, even less remarkable than the usual pelagic wanderings of the petrels and albatrosses, which follow the same ships for hundreds of miles in mid-ocean, although during portions of the year they are not without a "local habitation and a home," and probably never allow themselves to be led beyond certain definite boundaries. To account, however, for the long pelagic journeys of certain land-birds, it has been conjectured, and, perhaps, with some degree of probability, that they follow the ancient routes of the species, and that in remote times there were numerous islands along the line of present flight, which have disappeared by gradual subsidence, and that they derive
their ability now to pursue these routes | Among the raptorial birds, and in not a few through inherited experience. The existence of the common song-birds, the sexes are in many cases of such former landmarks paired on their first arrival, as appears to be and resting-places appears not improbable, generally the case with our bridge pewee, but to accept the explanation thus sug- and not unfrequently with the bluebird, the gested seems placing an almost unnecessary robin, and the Carolina dove. In such species burden upon the theory of the transmission it seems probable that the conjugal tie reof habit. mains unbroken through life, as appears to be certainly the case in most birds of prey. It is commonly believed, however, that the alliance between mated birds is of short duration, lasting only for a few months. is certainly true that the pairing season is often marked by fierce contests between rival males for the possession of favorites of the opposite sex. Yet the return of particular pairs of birds to the same nestingtree in species in which the arrival of the males precedes that of the females, as well as other circumstances, may well lead to the belief that in not rare instances the males are rejoined by their former partners.
In the autumnal migration, the young birds often, and in some species always, precede their parents, the interval varying from a few days to several weeks, according to the species. This has been claimed to indicate that it is folly to suppose that birds are guided in their wanderings by memory, as young birds, only three to five months old, can, of course, know nothing of the routes pursued by their ancestors, and yet find their way without difficulty. This, however, seems only to show that the instinct of migration is really transmitted habit, and that the knowledge of routes depends largely upon inherited rather than individual experience; for it should be remembered that if there is anything in heredity,—and that there is much in it seems beyond question,-it has operated through many thousands of generations in all migratory species of birds, and may therefore be supposed to have developed a potency that precludes the necessity of an acquired knowledge of routes through individual experience. That individual experience and memory, however, are important factors in the problem, seems evident from the facts already detailed in relation to the return of birds for many successive years to the same nesting-sites,-indisputable facts that admit of no other so probable, we may almost say evident, explanation.
While in the autumnal movement the young birds so often precede the old ones, the reverse, as already intimated, is the case in spring. If the physiological changes which characterize the approach of the reproductive season be presumably the stimulus of movement toward the breedingstation, nothing is more natural than that the mature birds should constitute the van. A further noteworthy feature of the spring migration is the frequent separation of the sexes during the northward journey, the males generally arriving somewhat in advance of the females, the interval varying somewhat with the species. This seems not in the least strange when it is considered that the initiative in all that relates to the continuance of the species devolves upon the male, in whom the sexual impulse is first awakened and is apparently stronger.
Closely connected with the general subject of migration are the erratic movements of birds-the casual or accidental appearance of individuals at localities far away from the usual habitat of their kind. Respecting such occurrences, two general facts are apparent: first, that in probably nine cases out of ten they occur at or near the time of the fall migration; second, that these waifs are almost always young birds, or "birds of the year." The appearance in New England, and even as far north as New Brunswick and Nova Scotia, of single examples of species whose true home is far to the south or west of even the middle portions of the United States, may be cited in illustration. In explanation of such erratic movements two suggestions immediately arise: either that these stragglers are true wanderers, which have inadvertently moved in a direction quite the opposite to that they should have taken, or, that they have been blown from their course while en route to their winter homes. While the fact of such wanderers being young birds might suggest their having taken a wrong direction, the same fact equally favors the theory of their having been carried by storms out of their true course, which their weakness and immaturity would enable them to resist less effectually than do the stronger adults. That the latter is the correct explanation of such phenomena is not only generally assumed, but seems to be borne out by the occasional appearance of North American birds in Europe under precisely similar circumstances, and the much greater
rarity of the occurrence of European species on this side of the Atlantic, the prevailing winds and the course of storms being, as is well known, from North America toward Europe. Still further proof, however, is afforded by the appearance in midwinter of species as far north as Massachusetts, and even Nova Scotia, whose home at this season is the Gulf States, or even Mexico. In the latter case, the inference! seems irresistible that such stragglers are carried upward by cyclones and borne rapidly and helplessly north-eastward to these distant points.
It is a popular belief that birds, especially certain northern species which in winter suddenly appear in temperate latitudes with or just before heavy storms, as well as various kinds of wild fowl, have the ability to discern approaching changes of the weather. While this idea has often been treated by scientific writers as fanciful, accumulative evidence shows that it has a basis in fact. Among such evidence may be mentioned the monthly weather reports of the United States Signal Service Bureau, in which, under the head of miscellaneous phenomena, reference is often made to the movements of birds. From these reports it, appears that the southward migration of geese and other water-fowl usually precedes, often by only a few hours, the approach of heavy storms, and a sudden and very great reduction of temperature, which they often wholly avoid by keeping in advance of
the change. Instances of this are too frequent to lead to any other conclusion than that birds have the power of recognizing approaching changes of weather. It is also well known that many birds display great restlessness just before the occurrence of severe storms, and that some species move southward in large flights to regions of less severity.
The general facts and conclusions presented in the foregoing remarks may be thus briefly summarized: 1st. That the habit of migration resulted from changes of climate occurring at a not very remote geological period. 2d. That every gradation exists between species the most widely roving and those which are strictly sedentary; and that even representatives of the same species may be either migratory or sedentary according to whether they occupy, as breeding stations, the northern or southern portion of the common habitat. 3d. That failure of food induces a movement toward warmer regions. 4th. That the return of birds to their breeding stations, which are their only true homes, is prompted by the recurrence of the season of procreation and strong home affection. 5th. That they usually pursue definite routes, and are guided in part by prominent landmarks, or by memory, and in part by "instinct” or inherited experience. 6th. That erratic movements are the result of transportation by storms. 7th. That birds discern approaching meteorological changes.
No sorrow such as mine the whole world wide
Till on the cruel cross I saw him die!
Be still and think, is this, thy young heart's woe,
I said, "O Mary! as thou lovedst thine,
I know she keeps him through the long years gone!
The Gate of Home.
O GRAVE, how still thou art!
O grave, how safe thou art!
By this low, peaceful shore,
O grave, stretch forth thine arms;
The desolate to rest.
Hope dead, to sleep in thee,
O grave, thou art the gate,
The flower-wreathed gate of Home; By thee the faithful wait, Until their chosen come. Shut me no longer out, O grave, from home.