374 THE ZOOLOGIST. 



seasons and unusual atmospheric disturbance, are confined chiefly 

 to unsuccessful and abortive attempts. It is maintained that the 

 height of flight is some 1500 to 15,000 feet; and if this be so, 

 as there seems every reason to admit, the aid of land bridges and 

 river valleys becomes of very slight importance. A trivial in- 

 stance will illustrate this. There are two species of Blue-throat, 

 Cyanecula suecica and C. leucocyana : the former with its red 

 breast patch is abundant in Sweden in summer, but is never 

 found in Germany, except most accidentally, as the other is the 

 common form of Central Europe. Yet both are abundant in 

 Egypt and Syria, where they winter, and I have, on several occa- 

 sions, obtained both species out of the same flock. Hence we 

 infer that the Swedish bird makes its journey from its winter 

 quarters with scarely a halt, while the other proceeds leisurely to 

 its nearer summer quarters. On the other hand, I have more 

 than once seen myriads of Swallows, Martins, Sand Martins, 

 and, later in the season, Swifts, passing up the Jordan Valley and 

 along the Bukaa of Central Syria, at so slight an elevation that 

 I was able to distinguish at once whether the flight consisted of 

 Swallows or House Martins. This was in perfectly calm clear 

 weather. One stream of Swallows, certainly not less than a 

 quarter of a mile wide, occupied more than half an hour in 

 passing over one spot ; and flights of House Martins, and then of 

 Sand Martins, the next day, were scarcely less numerous. These 

 flights must have been straight up from the Bed Sea, and may 

 have been the general assembly of all those which had wintered 

 in East Africa. I cannot think that these flights were more than 

 1000 feet high. On the other hand, when standing on the highest 

 peak in the Island of Palma, 6500 feet, with a dense mass of 

 clouds beneath us, leaving nothing of land or sea visible, save 

 the distant peak of Tenerife, 13,000 feet, I have watched a flock 

 of Cornish Choughs soaring above us, till at length they were 

 absolutely undistinguishable by us except with field-glasses. 



As to the speed with which the migration flights are accom- 

 plished, they require much further observation. Herr Gatke 

 maintains that Godwits and Plovers can fly at the rate of 

 240 miles an hour (!), and the late Dr. Jerdon stated that the 

 Spine-tailed Swift (Acanthyllis caudacutus), roosting in Ceylon, 

 would reach the Himalayas (1200 miles) before sunset. Cer- 

 tainly in their ordinary flight the Swift is the only bird I have 



