BRITAIN'S BIRDS AND THEIR NESTS. 207 



over small distances this does not seem to us to be greatly 

 exaggerated. Certainly it takes but a second or two for 

 the bird to sweep across a wide arc of sky visible from 

 some low - lying point of observation, and that, too, 

 although it may be flying many hundreds of feet above 

 us, and cannot easily disappear from our view. Often 

 the Swifts fly at great heights, circling above their nesting- 

 places on a summer evening, mere specks in the clear sky, 

 at an altitude of a thousand feet or more above the 

 ground. They spend most of their time in the air, 

 wheeling and circling for hours at a great height, or, at 

 a lower level, dashing past the house-tops in screaming 

 bands. No birds have such a combination of speed and 

 duration of flight, and to the Swifts we must surely 

 award the palm as the highest type of aerial animal, con- 

 sidered as such. It is probably to the Alpine Swift that 

 the absolute first place must be given ; but it is only an ex- 

 ceptional wanderer to these islands, and our smaller native 

 bird, its close congener, is scarcely inferior in prowess. 



Not only in the popular mind of to-day, but also in 

 the minds of capable naturalists of yesterday, Swift and 

 Swallow rank side by side as obvious cousins. But in 

 the light of modern researches this supposed relationship 

 is found to be altogether non-existent. There is merely 

 a superficial resemblance, caused by similar adaptations 

 to similar modes of life, such as we have already had 

 examples of. But in the more conservative internal struc- 

 tures the total absence of true relationship is at once 

 apparent. Into these matters we need not enter, but 

 one structural character claims our notice. In the 

 Swallow, three toes are pointed forwards, and the fourth 

 is long and pointed backwards. This arrangement is the 

 one best suited for perching. But who ever saw a Swift 

 perched on a telegraph-wire, one of the Swallow's favourite 



