THE ZOOLOGIST
No. 708.—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 distinguishing 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
