96 A HISTORY OF BIRDS 



birds can maintain themselves at an altitude of five miles, or 

 whether indeed they can attain this height, and this partly 

 on account of the low temperature which would be there en- 

 countered, and partly because the rarefied air would not serve 

 to sustain flight. This last is perhaps the more serious objection, 

 for cold would scarcely be felt by birds engaged in such violent 

 exercise as flight, while the clothing of feathers would be a 

 further protection. 



Birds on migration do not always, however, travel at a great 

 height, for there are occasions indeed when the exact opposite 

 is the case. Mr. W. Eagle Clarke, one of our greatest authorities 

 on all that pertains to these mysterious wanderings, has recorded 

 more than one occasion when enormous numbers of Larks, 

 Starlings, Thrushes and other small birds were crossing the 

 North Sea flying so low that they barely topped the crests of 

 the waves. On one such occasion when on the Kentish Knock 

 Lighthouse, during a gale accompanied by a downpour of rain, 

 the birds were scudding along after this fashion, apparently to 

 escape, so far as was possible, the force of the wind. And this 

 continued throughout the day, thousands and thousands passing 

 during this time. 



Estimates as to the height at which birds migrate sometimes 

 make large demands upon our faith, and this is no less true of 

 calculations as to the speed attained during their journeys. Thus 

 the late Herr Gatke, of Heligoland, one of the pioneers of the 

 study of migration, believed that the little Arctic Blue-throat 

 {Cyanecula suecicd) could leave Africa at dusk one evening and 

 arrive in Heligoland nine hours later, having travelled i,6oo 

 geographical miles in a single night at the astounding velocity 

 of 1 80 miles per hour ! According to another estimate of his, 

 Curlews, Godwits and Plovers crossed from Heligoland, to the 

 oyster-beds lying to the eastwards, a known distance of rather 

 more than four English miles, in one minute, or at a rate of over 

 240 miles an hour! Against such extravagant estimates it is 

 hardly necessary to attempt to bring rebutting evidence, but if 

 any be demanded this may be furnished by the Carrier Pigeon, 

 which has been known to maintain a speed of fifty-five miles for 

 four hours in succession ; and it is extremely unlikely that this 

 is much, if at all exceeded by wild species during long-distance 

 flights. 



