General Remarks.
The report for the East Coast of England shows that a great migration was carried on for six months in the autumn and winter of 1884-5. The schedules returned indicate that no one place had special preference, and that the inflow of migrants was equally distributed over the entire coast line.
The southerly movement of migrants was well established in July, and from this time to the end of the third week in January, 1885, there has been a steady flow, with slight intermissions, of birds either passing up the coast to the south or moving directly inland, the vast majority coming from the east across the North Sea, and moving westward or in westerly directions. Occasionally there have been heavy rushes or persistent bird waves continuous for days, and even weeks.
The periods of migration occupied by different species vary greatly, from four weeks to as many months; no general rule can be laid down in this respect.
As a rule, the young birds of the year migrate independently of the old, and some weeks in advance; there are, however, frequent exceptions to this, more especially late in the season, when the flocks are sometimes composed of old and young. With some of our shore birds, as Grey Plover, Knot, Sanderling, a few old birds, still in summer plumage, arrive very early in the season, some weeks later the main body of the young, and lastly the bulk of the adults, the latter having then assumed the ordinary winter dress.
The lines of migration have been those followed in previous years, the vast majority of immigrants coming either directly from east to west or from points south of east to others north of west. The records of birds travelling from points north of east are comparatively exceptional.
There was an immense and continuous rush, a gigantic feathery tide, on to the coast from the middle of October (15th) to the end of the month, migrants arriving continuously night and day. This rush was continued at some of the stations with but slight intermissions to the middle of November. The last fortnight in October is the average annual period of what may be called the "great rush" of immigrants on to the East Coast of England.
In previous reports we have drawn attention to the fact of a migration in opposite directions going on at the same time over the North Sea. This is observed more particularly at southeastern stations, on light vessels moored at many miles distance from the nearest land, where, during the spring and autumn, the same species of birds, as Crows, Rooks, Jackdaws, Starlings, Larks, Sparrows, Buntings and Finches, are recorded crossing the North Sea moving from opposite quarters and passing both towards the British coast and towards the Continent. This apparently abnormal movement in opposite directions is again indicated in the autumn and spring of 1884-5.
In a recent article in the 'Encyclopædia Britannica,' Professor Newton tells us that "there is scarcely a bird of either the Palæarctic or Nearctic regions, whose habits are at all well known, of which much the same may not be said; and hence we are led to the conclusion that every bird of the Northern Hemisphere is, to a greater or less degree, migratory in some part or other of its range." There can be no doubt that in this passage Professor Newton indicates the probable explanation of the special phenomena attending a double migration as recorded from time to time in our reports.
With very few exceptions, the vast majority of our British birds, such as are generally considered habitual residents, the young invariably, the old intermittingly, leave these islands in the autumn, their place being taken by others, not always necessarily of the same species, coming from more northern latitudes, or from districts of Eastern Europe, where, on the approach of winter, the conditions of locality and food-supply are found less favourable to existence. These immigrants on the approach of spring leave, moving back to the Continent on the same lines, but in the reverse direction to those traversed in the autumn; at the same time, also, our own birds return from the Continent to their nesting-quarters in these islands. To give one instance, out of many which might be cited, that of the Blackbird:—In the autumn, during September, the young of the year leave their summer-quarters, and their place is shortly taken by others, likewise young birds, coming in October and November from districts which lie directly east or south-east of Great Britain. Should our English winter prove generally severe, or even partially so, our old birds will also leave, and in their place we have an influx of old Blackbirds from the Continent, pushed forward by similar causes. In the last autumn and winter, which has been exceedingly variable, with many sudden changes of temperature, our East Coast reports show an enormous migration of this species to have taken place. This commenced on September 12th, and was continued at intervals throughout October, becoming nearly continuous in November; after this intermittent, in throbs and pulsations, up to the end of the third week in January, 1885. These influxes of old birds correlate with sudden changes of temperature and outbreaks of severe weather on the Continent. In the spring the continental visitors disappear, and our so-called resident Blackbirds come back to their nesting-quarters. In this way we have a regular interchange of birds in the spring and autumn,—a double migration, carried on twice a year between the British Islands and the Continent. As far as our knowledge extends the normal conditions of locality and climate over the whole area are such as do not necessitate a regular interchange of the members of their respective avi-faunas. There is apparently no reason why our Rooks, Starlings, Sky Larks, and Blackbirds should not be able to winter in England just as well as abroad; their not doing so, but persistently migrating, is suggestive of a regular succession of bird waves,—as one moves forward another quickly follows in its wake. The southern limit of autumn migration, in the individuals of any species, is in direct ratio to the breeding range; such as nest in southern latitudes move still further south, and thus make room for those of their sort which have nested further north. Such are the ordinary phenomena of migration, a movement which is as regular and persistent as the flow and ebb of the tide.[33]