The Migration of Birds/Chapter 10
CHAPTER X
SUGGESTIONS AND GUESSES
Several important migration phenomena have hardly been touched upon in the previous pages; a few words about these may not be out of place
There is no doubt that now and again American species are met with in Europe, and European in America, though there is no evidence of direct regular trans—Atlantic passage, except from Greenland. The appearance of these birds has been explained in several ways, the general notion being that it is impossible for a bird to fly unaided across the Atlantic, say over 3000 statute miles, without rest. In considering the question we are met with various points on which we still lack knowledge.
We know that strong-winged waders can accomplish 2500 miles, apparently without a rest, and that if rest is necessary these birds can swim and rise from the waves. We know, too, that there is regular passage between Greenland and Europe. We do not know how long a bird can, without rest and food, sustain flight; we do not know the speed it can travel when aided by favourable winds, nor to what extent even passerine birds may rest upon the water. My friend Mr J. A. Dockray, when punting in the Dee estuary, has often seen birds alight to rest on his punt, and once saw a tired thrush Settle repeatedly on the water and finally safely cross the estuary. There are several instances recorded of passerine birds alighting upon and rising again from the water.
We do not know the extent of Greenland as a summer breeding home of birds; the growing knowledge of this vast continent proves that its summer avifauna is much larger than we thought, and that western and eastern forms inhabit adjacent breeding areas; the possibility of birds banding with the wrong set of travellers is greater than was suspected.
It is urged that the western shores of Scotland and Ireland should receive these stragglers, but that the records of American birds are fewer from these coasts than from the eastern shores and even Heligoland. The best island route, however, would lead birds to join the travellers from Scandinavia which pass by the safer eastern route than the one round the western wind—swept shores of Ireland. Even this reputed scarcity may be error, for how many reliable watchers are there compared with the immense length of this wave-indented coastline? How easy for a straggler to be overlooked! Mr S. F. Baird, in his paper on the "Distribution and Migration of North American Birds," is emphatic that the transfer of American birds to Europe is entirely due to the agency of winds carrying them from their course (6). Mr A. L. Butler met with snow-buntings in mid-Atlantic travelling east, and Mr J. Trumbull supplies information about many passerine birds—especially snow-buntings and wheatears—seen in September and October at various points between Canada and the British coasts (53). Some joined ships but others made no attempt to do so, even at 54" north 44° west.
Unfortunately there is the negative evidence of fraud, for when unscrupulous dealers found that the public would give high prices for rare birds, a trade in American skins began. It is not impossible that even Gätke was victimised. Error or even accidental fraud may be taken into account. Some years ago I heard that a hawk-owl had been killed in Cheshire, at an inland port on the Ship Canal; I traced the bird, the American species, but discovered that it had been captured on an east-bound steamer in the Straits of Belle Isle, and had only died or been killed when the vessel reached the cooling station at Partington, where the taxidermist who received it thought it had been taken. A Cape pigeon, which I saw in the flesh, reported as shot in Lancashire, I found had been brought home in cold storage.
Birds may be carried on ship-board When the "Mauretania" was between 400 and 500 miles out from New York, bound eastward on June 15th, 1911, a Curlew came on board and remained for three days, leaving when the Irish shores were sighted on the 18th. My informant, an experienced wildfowler, failed to catch the bird, but described it as like our curlew. Probably it was the American Numenius longirostris[1], but amongst the Irish curlews it would easily remain unrecognised.
When a seabird appears inland the usual explanation given is "storm-blown," but increasing knowledge shows the frequent fallacy of this idea. The Manx shearwater, for instance, is a regular migrant, and the examination of the dates of the records of so—called "storm-blown" birds found in inland localities shows a remarkable regularity; the majority are met with between the and of August and the end of the first week in September. Not only do the birds move south in the early days of September but many, usually at any rate, cross England; the weaklings fall out and are found. Is it possible that some of these collapses of passing birds are due to more than mere physical fatigue? Aviators have discovered the existence of "wind pockets" or "holes in the air," where the resistance of the air appears suddenly to fail; what is the effect on a flying bird which suddenly enters one of these pockets?
The lesser black-backed gull also Crosses England in large numbers; its movements are more noticeable than those of the herring gull, common gull, or even of the inland nesting and inland feeding black-headed gull.
Recent investigation has added the yellow-browed warbler, the blue-throat, and many other "rare," or "casual" passerine birds to the list of regular British birds of passage; evident1y they have been overlooked before, Even the crossbill, so long classed as a spasmodic invader, is now seen to be a regular bird of passage to Britain, though in varying numbers, and quite independently of the sub-specific form which is always with us.
The wanderings to our islands of southern petrels and other oceanic birds has occasioned much surprise. Take two examples of the genus Oestrelata, one O. brevipes[2] taken at Earth in 1889, and O. neglecta[3] in Cheshire in 1908, the known breeding range of both being in the western Pacific; pelagic wanderings might lead a bird anywhere, but it is conceivable that investigation may show that the breeding area is wider than is supposed and that these species have stations even in the South Atlantic.
Some writers affirm that birds only migrate on the wing, but the journey by sea of many species is varied in method. Those very regular migrants, the puffins and guillemots, which the light keepers assure us leave and return to their stations almost at fixed dates, move by slow nautical stages, swimming and feeding as they go, On May 2nd, 1911, I watched a red-throated diver slowly travelling north; it actually travelled farther beneath the surface than either by swimming or flying, so long as I had it in view. The penguin's migrations cannot possibly be on the wing. Dr Brooks rightly contended that the periodic assemblage of wandering sea-birds at their "rookeries" is true migration, regular as the almanack, although the feeding area is immense and the birds do not reach home by any single path. Seebohm tells us of young bean geese migrating in full moult, marching in an army to the interior of the Tundra, and Mr W. H. Hudson, in "Birds and Man," relates a pathetic story of a pair of upland geese in southern Buenos Ayres. His brother saw them in August, the early spring of South America, leaving the plains where they had wintered to breed in Magellanic islands. The main flocks had departed, but these two birds, the female with a broken wing, were steadily moving south, the male taking short flights and waiting for her, as if to urge her on, and the female walking "And in this sad, anxious way they would journey on to the inevitable end, when a pair or family of carrion eagles would spy them—and the first would be left to continue the journey alone."
- ↑ Long-billed Curlew, now known as Numenius americanus. (Wikisource contributor note)
- ↑ Collared Petrel, now known as Pterodroma brevipes. (Wikisource contributor note)
- ↑ Kermadec Petrel, now known as Pterodroma neglecta. (Wikisource contributor note)