BRITISH BIRDS OF FASTEST FLIGHT 53 
the subject with me, agrees that the spine- tailed 
swift is the faster flier, and tells me that he thinks 
it is probably the heavier bird of the two, and that 
this may account for its greater rapidity of flight. 
The wing of the Alpine swift is 8-45 inches, 
that of the spine-tailed swift is 81 inches. The 
length of both birds is 8 inches,^ although Dresser ^ 
gives the total length as 8-5 and that of the 
spine-tailed swift as 8-1 inches. 
The genus Chaetura, to which the needle- 
tailed swift belongs, is easily distinguishable from 
the genus Apus (to which the common swift and 
Alpine swift belong) by the wedge-shaped tail in 
which the shafts of the feathers are longer than 
the webs and protrude like spines. The tail in 
the only species {Chaetura caudacuta caudacuta) 
occurring in the British Isles, compared with that 
of the Alpine swift, is very short. It is almost 
square, and has ten feathers, which are very stiff 
and the shafts of which project 4-6 mm. (-156- 
•234 inch) beyond the web in a stiff point like that 
of a needle or spine. ^ 
^ Manual of British Birds, by Howard Saunders, 2nd ed. (Gurney 
& Jackson, London), pp. 264, 266. 
* History of the Birds of Europe, by Henry E. Dresser, F.L.S., F.Z.S. 
(1871-1881), vol. iv. p. 617. 
^ A Practical Handbook of British Birds, edited by H. F. Witherby, 
vol. ii. pp. 7, 9. Witherby & Co., London, 1920. 
