Page:The Migration of Birds - Thomas A Coward - 1912.pdf/143



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