CHAPTER IV
THE HEIGHT AND SPEED OF MIGRATION FLIGHT
In the last chapter reference was made no the great height at which birds may fly on migration. Certain species, even comparatively weak-winged ones, appear normally to fly high, Whilst others, Often birds with pointed Wings and great aerial powers, usually proceed at low elevations; but there is still much conjecture as to the actual altitude reached by any migrants.
Gätke was of opinion that we do not see much of real migration, which is certainly correct, but there is no reason for his statement that it normally takes place at anything like the altitudes he mentions, 30,000 feet or more, or that birds at the time of migration undergo physiological changes which enable them to fly at immense heights and speeds and to see clearly in the dark (29). Nor need much weight be placed on the speculation of Lucanus, who contends that the height of travel must be less than 1000 metres, for above that elevation aeronautical observations show that perspective lessens. There are actual observations which, though liable to a margin of error, are proof of migratory flight at very high altitudes.
