BIRDS THAT PASS IN THE NIGHT.
THE results of eight years' observation of the migration of birds into and out of this country has just been issued by the Council of the British Association. It appears oppor- tunely, at the moment when the rush of our summer birds southwards to other lands is at its height, and the corre- sponding stream of immigration from the North is within a few weeks of its greatest volume. The facts which it chronicles are fall of interest, and though the author of the report refrains from stating any views as to the causes of migration, or the intelligent forces which guide or sug- gest the journeys of the birds, a clue has been found to account for the knowledge apparently possessed by birds that on a given day, in distant and frozen regions, the earth will be open and accessible.
The object of the inquiry which has been going on round our coasts for eight years was simply to find out what birds come to and go from this country across the sea, and when they do so. The means to do this were almost perfect. The millions of pounds which commerce has spent to surround the coast with lighthouses and lightships were simply "con- verted" for these years to the use of the naturalists. It coat little or nothing. The Elder Brethren of the Trinity House, the Commissioners of Northern Lights, and others fell in with the idea. The lighthouse-keepers were delighted to vary the monotony of their lives by watching the birds, and took to the work of "filling in reports" with the carious liking which all fairly educated working men, such as railway guards, porters, and policemen, now evince at the chance of "filling in returns." Though all the men were volunteers, the reports were "surprisingly acourate,—it is wonderful how the observations at one station were borne out by those taken at others." From this ready-made girdle of watch-towers, with guards whose duty kept them vigilant at night, from year's end to year's end, for a period only shorter by twelve months than that for which Clytemnestra's sentinel sat waiting to light the beacon telling of the fall of Troy, the records have been
sent of the owning and going of the birds. And the record is perfect and unbroken. It is synoptic. The returns showed what birds were coming and what going, from every part of If our islands lay under the trade winds, where the weather constant, or in a different part of Europe, the results of this complete means of observation would probably be simple and conclusive. But as England so lies in the ocean as to be both astopping-place and a " crossing-place" for birds passing to and from S iandinavia to South Europe and Africa, and to and from the Continent to Ireland and Spain, our "migration" is as muddled as our weather, which, in. stead of being constant, is always being upset by cyclones 'from the Atlantic. On the other hand, the number of the returns, and the industry of Mr. Eagle Clarke, who has compiled the report, afford material for discovering the main facts even of those complex bird-movements. We give some of theft shortly, not that they are specially interesting in themselves, but because they stand in relation to conditions of weather and temperature, which, when placed *together, and in their relation to the birds' journeys, appear very much in the light of a discovery. In September and October, when the English nesting-birds, such as the swallows, are gathering together and flying south, the birds of Norway, Sweden, and Iceland are pouring in on the East Coast. The close chain of lighthouses on this coast shows that these northern birds do not hit our shores lower than Cromer. They drop in from Shetland to the end of the northern jut of Norfolk, but not further south. On the other hand, another -stream comes from Denmark, North Germany, and Holland into the month of the Thames—Essex and Kent—and separating, passes right up the East Coast as far as the Tees, and down the Channel towards Cornwall. The greater number are starlings, larks, plovers, and rooks The rook thus appears thoroughly migratory, and the story of the flock which used to fly across the Channel once a week from a Sussex rookery does not appear so improbable as it did. The birds coming by this last route always arrive in the daytime, and in no case are the immense flights of birds observed passing to and from these islands which Dr. Giitke and Mr. Seebohm saw in Heligoland. There the streams seem con- centrated. Here they are dispersed, and simultaneous observa- tions taken show that there is little or no connection between the routes taken over England and that which crosses the great carrefour of migrating birds, the little island reek off the Elbe. Details of the arrival and departure of the various species will be found in the report ; but the details of mass migration are apt to perplex counsel, while the details of the actual journey of any particular species, such as the swallows, and their journey from England to the Equator, are not yet made out, though Mr. Eagle Clarke offers to do so in a further report. We pass on to what seems to us to be the most interesting result of the present set of observations. *Outside and inside the ring of lighthouses the Committee had another body of information of the most important kind. T.heyliad the weather-chart of the Meteorological Office. If any one takes the Times' weather-chart, and draws a red circle round the coasts of England, Ireland, and Scotland, this will represent the ring of stations recording the arrival and depar- ture of the birds. Outside this is a wide region, from the North Cape to the top of Corsica and the Pyrenees, over which our Meteorological Office daily notes the weather in its chart. Thus, when the grey orows and fieldfares are arriving at Sand- ringham we know exactly what the weather was like in Norway when they started, and over the North Sea when they were flying. So we know what the wind, barometer, and tem- perature were like in France when the flights of spring migrants reach the Start. In this double record we can compare both the daily weather of North Europe and the daily movements -of the birds in a central part of that aeea. The result is most suggestive. Nearly the oldest scientific notice of migration is a note in the "Floral Calendar" of Theophrastas, that the birds come to Greece on the "orni- thian winds" 'between February 20th and March 12th. As at was the oldest, so it is the longest lived of beliefs about migration, that the birds wait for favouring winds. The weather-chart shows that they do not. The direction of the wind is disregarded. "It is no incentive to migration." On the other -hand, heavy gales stop migration entirely. The birds dare not move, and the ocean species, such as the petrels, are caught and driven inland in heavy gales. Ordi- nary steady winds they simply disregard. In other words, what the birds observe is not wind, but "weather." When the hurrying cyclones are crossing the Atlantic, or travelling round the Shetland Islands and on to the Norwegian coasts, the birds do not move. "The stream of migration is dammed up at its source ," and when released the birds rush over in a torrent. The great congregations of swallows noted at the end of the first fortnight of September, not only on the Thames eyots, but on the Rhine, had been waiting till the cyclonic gales of the first fortnight of September (which wrecked houses in Paris and Manchester) were over. Since then the migration has been normal, and in smaller flocks. So in October, as soon as a period of still, " anti-cyclonic " weather with cool temperature begins in Norway, the birds set out for England. They come here on an easterly wind, not because they started with it, but because the calm "anti. cyclonic area" in Scandinavia has easterly breezes on its edge where it lies over the North Sea. If it is not wind which the birds wait for, we may ask what other weather conditions besides the absence of storms is an incentive to migration. The answer given by the charts is temperature. It is tem- perature which is the main controlling factor in all the great movements. Cold coming in the calm anti-cyclone sends them south. Warmth, and a rising thermometer, is the instant signal to go north. A fact noted by Mr. Eagle Clarke shows the sensitiveness of birds to the rise of tem- perature, and the way in which, with their swift flight, they follow the warmth as a shadow follows smoke. On February 17th, 1887, wheat-ears and a ring-ousel were seen near the Chicken Rock Lighthouse and the Longship Station. This was strangely early for these birds to come, but a reference to the daily weather-report showed that this portion of the British area was the warmest spot in Wetter,' Europe on that particular day ! It is easy to conceive that birds fly from the North before the cold. But the standing problem of migration is their almost instantaneous arrival inside the Arctic circle from the South when the frost first gives. Mr. Seebohm noted that in the valley of the Petchora they came in twenty-four hours after the warmth began. The explanation seems to be that temperature may quickly rise over great areas. The birds at the furthest extremity instantly note the change, and in the course of a day's flight reach the northern fringe, where, as Mr. Seebohm showed, a store of ice-preserved fruit, and of insects released from the egg at the first touch of warmth, awaits them.
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