1912. Revietv, 201 



REVIEW. 



HOW DO BIRDS FLY? 



The Flight of Birds. By F. W. Headley, M.B.O.U. With 16 plates, 

 and many text -figures. Pp. 163. London ; Witherby and Co., 

 19 1 2. Price 5s. net. 



The mechanics of bird-tiight are very well explained in this small volume, 

 which has admittedly been written with a view to enlisting in some degree 

 •the interest of the bird's human imitators. Many effective photographic 

 illustrations are given, showing different phases of flight and different 

 forms of wing ; and the study of the subject should receive a desirable 

 stimulus from Mr. Headley's simply-written and suggestive treatise. 



That there is much still requiring to be learnt is fully acknowledged. 

 We should have liked to see some attention shown to the variations of 

 wing-formula as between different species of birds, with some suggestions 

 as to their bearing on flight requirements. We can hardh^ doubt that 

 some purpose is served by such variation, when we find, for instance, the 

 third primary invariably the longest in the Common Redstart and the 

 Whinchat, but the fourth in the Black Redstart and the Stonechat. Is 

 it because the two last-named species make shorter migrations than their 

 respective congeners that the apex of the wing is thrown back in each case 

 by the breadth of one quill-feather ? It would be of considerable interest 

 to see the question discussed ; but Mr. Headley probably deems the time 

 not yet ripe. Again, is it of any importance to the Chiffchaff to have four 

 of its primaries " emarginate," while the Willow-Wren has but three, and 

 the Wood-Wren two ? So far as we can see, the whole use of the dis- 

 tinction is to the ornithologist, who values it as a means of telling one of 

 these little birds from another — especially if he safeguards his memory with 

 the coincidence that the Chiffchaff's four emarginate primaries correspond 

 with the four f's of its name, while the Willow-Wren's three correspond 

 with its three w's, and the Wood-Wren's two with its two o's. 



Mr. Headley devotes some interesting pages to the velocity of the 

 migratory flight, which he believes to be far greater than that of the 

 ordinary flight. This is probably true in the case of many species, for. a 

 bird during ordinary flight has seldom much motive for putting on its 

 utmost speed. The ordinary flight of a Swift is certainly nothing to what it 

 can do when in danger of being overtaken by darkness on its way home 

 from a distant excursion. The author also believes that birds on migration 

 frequently derive important assistance from a tail-wind, to get into which 

 they may mount to extraordinary heights. Mr. Headley has collected 

 a considerable number of interesting observations with an indirect bearing 

 on this question, and a direct one on that of the height at which migrants 

 fly. It must, however, be sufficiently clear that most migrants are able 

 to dispense with this tail-wind assistance, however convenient they may 

 find it on occasions. 



