Those who have read the absorbing pages of Darwin devoted to the consideration of the sexual characters of birds, or know the examples given by Buechner, Audubon, Epinas, Wallace and other naturalists, or, better still, those who have watched and noted for themselves the love-habits of birds, will find it impossible to withhold admiration for the poetic character of many of these courtships and marriages, which put too often our own human matings to utter shame. Let us look first at the love-dances. Dancing as a means of attracting the right pitch of passion in the male and the female has always been used in the service of the sexual instinct. It gives the highest and most complex expression of movement, and may be said to have been evolved by love from the more brutal courtships of battle display.[60] The characteristic features of the amatory dances of birds are well known; they may be witnessed frequently during the pairing season. The male blackbird, for instance, is full of action as he woos his mate; he flirts his tail, spreads his glossy wings, hops and turns; chases the hen, and all the time chuckles with delight. Similar antics are performed by the whitethroat. The male redwing, again, struts about before his female, sweeping the ground with his tail, and acting the dandy.[61] The crested duck raises his head gracefully, straightens his silky aigrette, struts and bows to his female, while his throat swells and he utters a sort of guttural note.[62] The common shield duck, geese, wood-pigeons, carrion-vultures, and many other birds have been observed to dance, spread their tails, chase one another, and perform many strange courting parades. A careful observer of birds, Mr. E. Selous, who is quoted by Havelock Ellis,[63] has found that all bird dances are not nuptial, but that some birds--the stone-curlew (or great plover), for example--have different kinds of dancing. The nuptial dances are taken part in by both the male and female, and are immediately followed by conjugation; but there are as well other dances or antics of a non-sexual character, which may be regarded as social, and these too are indulged in by both sexes. The love-fights of swallows, linnets and kingfishers, and the curious aerial evolution of the swift are similar manifestations of vigour and delight in movement[64] as a sexual excitant to pairing. Some male doves have a remarkable habit of driving the hen for a few days before she lays the eggs. On these occasions his whole time is spent in keeping her on the move, and he never allows her to settle or rest for a minute except on the nest.[65]