The Zoologist/4th series, vol 4 (1900)/Issue 704/On Sexual Differences in the Wing of the House-Sparrow (''Passer domesticus''), Butler

by Arthur Gardiner Butler

 

ON SEXUAL DIFFERENCES IN THE WING OF
THE HOUSE-SPARROW (PASSER DOMESTICUS).

By Arthur G. Butler, Ph.D., &c.

 

In a short article on the wing of the Sky-Lark, which I published in 'The Zoologist' for 1898, I expressed my intention of noting the sexual differences in wing-structure of other species. Mr. C.H.B. Grant again assisted me with wings of three male and three female specimens of the domestic Sparrow; I already possessed five others, and subsequently Mr. F.W. Frohawk added to my collection. I therefore thought I could not do better than select this as an additional example in proof of the fact that, as a rule, the wings of male birds are better adapted to swift flight than those of their mates, thus enabling the former to overtake the latter when courting.

Of the six wings which Mr. Grant secured for me, all are carefully labelled, but in five of them the important note is added of the actual length of the bird in the flesh from which the wing was removed. As will at once be seen, this is a point of considerable importance, as it proves that, although individuals vary slightly in size, there is no great discrepancy in the total length of the sexes in the flesh. The following are measurements of three males:—

Females	⁠	1. Total length		63⁄8 inches.
		2.⁠„⁠„⁠		61⁄4⁠„
		3.⁠„⁠„⁠		61⁄8⁠„

Of two females the measurements are:—

Females	⁠	1. Total length		61⁄2 inches.
		2.⁠„⁠„⁠		61⁄8⁠„

Comparing the expanded wings of the sexes in the same specimens, we get the following interesting results:—

Males	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	1. Total length		41⁄2 inches.
		2.⁠„⁠„⁠		33⁄4⁠„
		3.⁠„⁠„⁠		35⁄8⁠„
Females	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Total length		31⁄2⁠„
		⁠„⁠„⁠		37⁄16⁠„

Thus the largest hen, although a bigger bird than the largest cock, measures half an inch less in entire length of wing, this difference being due entirely to the lengthening of the second to the fifth primaries, with their coverts, in the male birds. These same feathers are often, though by no means invariably, narrower in the females than in the males, and when this is the case the resisting power of the wing must be considerably weakened.

The width of the wing from back to front shows little, if any, sexual difference, the secondaries being about of equal length in male and female; the natural effect of breadth without correspondingly developed length would be to produce a somewhat heavier and slower flight, so that in every respect the male bird has the advantage.