But it is particularly among birds that the sentiment, or rather the passion, of love breaks out with most force and even poetry. It is especially to birds that the celebrated Darwinian theory of sexual selection applies. It is difficult, indeed, not to attribute to this influence the production of the offensive and defensive arms, the armaments, the organs of song, the glands of odoriferous secretion of many male birds, also their courage, the warlike instinct of many of them, and lastly, the coquetry of the females. Let us listen to Audubon, as he relates the loves of the skylark:--“Each male is seen to advance with an imposing and measured step, swinging his tail, spreading it out to its full extent, then closing it again like a fan in the hands of a fine lady. Their brilliant notes are more melodious than ever; they repeat them oftener than usual as they rest on the branch or summit of some tall meadow reed. Woe to the rival who dares to enter the lists, or to the male who simply comes in sight of another male at this moment of veritable delirium: he is suddenly attacked, and, if he is the weaker, chased beyond the limits of the territory claimed by the first occupant. Sometimes several birds are seen engaged in these rude combats, which rarely last more than two or three minutes: the appearance of a single female suffices to put an instant end to their quarrel, and they all fly after her as if mad. The female shows the natural reserve of her sex, without which, even among larks, every female would probably fail to find a male [this is a little too flattering for larks, and even for men]. When the latter,” continues Audubon, “flies towards her, sighing forth his sweetest notes, she retreats before her ardent admirer in such a way that he knows not whether he is repulsed or encouraged.”[5] In this little picture the author has noted all the striking traits of the love of birds--the courage and jealousy of the male, his efforts to charm the female by his beauty and the sweetness of his song, and finally, the coquetry of the female, who retreats, and thus throws oil on the fire. The combats of the amorous males among many species of birds have been observed and described minutely. “The large blue male herons,” says Audubon, “attack each other brutally, without courtesy; they make passes with their long beaks and parry them like fencing masters, often for half-an-hour at a time, after which the vanquished one remains on the ground, wounded or killed.”[6] The male Canadian geese engage in combats which last more than half-an-hour; the vanquished sometimes return to the charge, and the fight always takes place in an enclosed field, in the middle of a circle formed by the band or clan of which the rivals form part.