A short bibliography is given at the end of the present volume, including the more important works on the subject and a few of the papers in periodical publications referred to in this manual.
[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.