The Descent of Man

Various birds have spurs on their wings. But
the Egyptian goose (Chenalopex aegyptiacus)
has only "bare obtuse knobs," and these probably
shew us the first steps by which true spurs
have been developed in other species. In the
spur-winged goose, Plectropterus gambensis,
the males have much larger spurs than the females;
and they use them, as I am informed by
Mr. Bartlett, in fighting together, so that, in this
case, the wing-spurs serve as sexual weapons;
but according to Livingstone, they are chiefly
used in the defence of the young. The Palamedea
(Fig. 38) is armed with a pair of spurs on
each wing; and these are such formidable weapons
that a single blow has been known to drive
a dog howling away. But it does not appear
that the spurs in this case, or in that of some of
the spur-winged rails, are larger in the male
than in the female. (16. For the Egyptian goose,
see Macgillivray, 'British Birds,' vol. iv. p. 639.
For Plectropterus, Livingstone's 'Travels,' p.
254. For Palamedea, Brehm's 'Thierleben,' B. iv.