BIRDS 



lOI 



are still obscure, but Gatke's calculation must be too 

 high, and we will turn to safer figures. We know from 

 exact observation that wild ducks can fly more than 

 forty-seven miles an hour, and carrier-pigeons seventy- 

 two miles an hour. The highest known speed was 

 reached, according to a careful experiment, by a house- 

 swallow, which travelled from Ghent to Antwerp in 

 1 2 "5 minutes, and so must have done i86 miles an hour. 



The bird can, of course, increase or lessen the speed 

 of its flight, according to need. Hence these figures 

 cannot tell us anything certain with regard to the 

 speed of migration. We know little, moreover, as to 

 the duration of the migration. It seems that many birds 

 make a halt at suitable spots, but others continue their 

 flight without interruption to the end, while the weather 

 permits. 



It is marvellous how a bird can maintain such a 

 velocity so long, yet we never see any signs of fatigue 

 in migratory birds. It is only a violent storm that 

 distresses them, and if they are surprised by one at sea 

 thousands of them may perish in the waves. Many 

 species of land-birds can alight in a calm sea without 

 being drowned. Gatke has seen the snow-bunting, the 

 mountain-finch, and the thrush do this. 



Most ornithologists believe that it is the altitude at 

 which the migration flight takes place that enables birds 

 to make such long stretches ; they say that the birds 

 meet less resistance in the upper air. We are also often 

 reminded of the special adaptation of the bird for flying 

 — the air-sacs that are found in its body and the bones 

 filled with air, which increase the volume of the animal 



