"Besides hooded crows, many other, indeed perhaps all species, are capable of executing a laterally-directed movement of flight of this nature, not only under such compulsory conditions as they may encounter during the flight of migration, but also during the ordinary activities of their daily life" [(29)]. He admits that he once thought it was a drift to leeward, but that he is now convinced that it is intentional, and is sure proof of his East to West flight. In the face of such absurd statements as these, how can anyone quote Gätke as an authority on migration! Yet, in recently-published books, this east to west flight across Heligoland to Yorkshire is stated to be a proved fact, though Mr Eagle Clarke, so long ago as 1896, showed it to be unsupported by British evidence.
Dr Allen, reviewing Dr H. E. Walter's "Theories of Bird Migration" [(3)], cites the following experiments as strong arguments in favour of orientation. Dr J. B. Watson took fifteen sooty and noddy terns from Bird Key, Tortugas, and liberated them at intervals after they had been marked. The shortest distance was 20 miles from the Key, the farthest, Cape Hatteras, 850 miles; thirteen returned to the Key. Neither sooty nor noddy terns range, as a rule, north of the Florida Keys, so that it is unlikely that any of the birds had been over the route before. They could have gained no experience, or hereditary knowledge, and as they were released during the breeding season, there would be no marked movement southward which they might follow, nor would they at that time be impelled by any desire to migrate. The change of direction from the Florida Keys, westward, to the Tortugas, occasioned by the water course which feeding habits would force them to follow, "removes the direction of the wind as a guiding agency, whilst the absence of landmarks over the greater portion of the journey makes it improbable that sight was of service in finding the way."
[CHAPTER VI]
THE DISTANCES TRAVELLED BY BIRDS
Not only do the distances of the migration paths of different species vary considerably, from a trip of a few miles to a voyage from the Arctic to the Antarctic, but the individuals of one and the same species do not all travel to the same degree.
The familiar swallow, Hirundo rustica, though subject to certain geographical variations, is found throughout the Palæarctic and Nearctic regions, nesting throughout Europe to between 63° and 70° north and in Africa north of the Sahara, where, however, Canon Tristram found it also wintering in the oases. South of the Sahara to the Cape it is a winter visitor. In Asia it breeds, according to Seebohm, in Asia Minor, Persia, Afghanistan, and western Siberia, and winters in Scinde and western India. One form breeds in and north of the Himalayas, eastward to China and Japan, and winters in India and Burma, and another ranges from eastern Siberia across Behring Strait throughout North America, so far south as Mexico. This form winters in Burma, in Central America and Brazil, but the Mexican birds are more or less stationary at all seasons.
Our swallow and its congeners have an almost cosmopolitan range, summering in the Northern and wintering in the Southern Hemisphere or comparatively near to the Equator in the Northern. Towards the centre of its range its migrations are either short or the bird is non-migratory.
Mr W. L. Sclater, addressing the South African Ornithologists' Union [(42)], stated that the swallow arrives at Cape Town at the end of October, and is common from November to March; practically all have left by the middle of April. Swallows begin to arrive from the south in Africa north of the Sahara in the latter half of February; early in March they reach southern Europe, later in the same month they are in Central Europe and by the middle of April large numbers arrive in England. Thus swallows leave South Africa actually after they have arrived in England; the South African birds cannot be the same which are in North Africa a month earlier! The swallow supports Seebohm's thesis that the individuals which go farthest to the south in winter, breed farthest north. A day-migrant and by no means a rapid one, the swallow may be timed from place to place, and it is not presumption to suggest that the birds which reach Britain to nest came from lands little south of the Sahara and well north of the Equator, and that those which pass through England and along our shores in May and even June are on their way from Southern Africa to the northernmost limits of their range. Mr Sclater points out one very interesting fact; when the swallow reaches South Africa it is in ragged worn plumage, before it begins its northward journey it passes through its one annual moult.