THE ZOOLOGIST 



No. 70 8. —June, 1900. 



ON SEXUAL DIFFERENCES IN THE 

 FEATHERING OF THE WING. 



By Ed. Degen. 



Under this heading Dr. A. G. Butler has published (Zool. 

 1898, pp. 104, 105) his observations made on the Sky-Lark 

 {Alauda arvensis), and more recently again (ante, pp. 74, 75) the 

 results of his investigations in regard to the House-Sparrow 

 (Passer domesticus) . Unquestionably any additional knowledge of 

 birds whose plumage, on account of the great similarity existing 

 between the two sexes, offer such great difficulties in distinguish- 

 ing between them, as the Sky-Lark and many others, will be not 

 only appreciated by the aviculturist, but also by the ornithologist 

 and student, the fuller such information is afforded. That 

 differences in the area of the bird's wings of the two sexes exist, 

 at any rate for the species referred to above, has been shown by 

 Dr. Butler in the respective dimensions of their wings. More 

 important, however, are the deductions he makes therefrom, 

 other than mere sexual differentiation ; especially when he calls 

 attention to a possible advantage in power of flight acquired by 

 the male bird over the female, induced by a slight increase 

 in the wing-feather area — in those cases, at least, as he points 

 out, where a reduction in the weight of the body, as in the male 

 Dunlin, does not take place. 



As I happen to possess a series of over thirty specimens of 

 Zool. 4th ser. vol. IV., June, 1900. s 



