Campaign Diary: A Tranquil Scene Masking a Dark Contest | Birds

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An quacking rash of a female mallard duck catches my eye on the Lagan River. Two pairs. Further, two single males. Familiarity may breed rejection of “Oh, it’s just a…” but the mallard is a splendid creature.

My gaze falls on a bottle-green head, its sunny iridescence blending with the reflected sheen of the water to shimmer through its feathers. The primary yellow beak. The thin white collar on his chocolate-colored chest. The finely vermiculated porcelain gray and taupe running down to the rump, with its reverse curls and white tail wedge. Its mate’s plumage is an embroidery of browns, but it shares with it a bright blue flash on the secondary wing feathers, called the speculum.

The reeds are swaying. Three more drakes emerge on the open water. A loitering female swims quickly to catch up with her mate. His caution is wise. This tranquil scene masks a dark contest. The sex ratio of mallard populations is skewed towards males, and excess males gang up to intimidate females into what biologists coyly call “forced copulation.” This is something that I always find disturbing. Female mallards usually resist, but may even end up drowning. Staying close to its mate provides some protection until the ducklings hatch; whereupon their father decamps, perhaps to join a band of marauding bachelors.

Drakes are successful in mating with reluctant females in part because, as an ancient evolutionary group, duck species have retained the avian penis, which is highly unusual in birds (for most species the transfer of sperm relies on a cooperative genital “kiss”).

But that’s not the whole story. Nature managed to provide female mallards with built-in contraception. The vagina has a spiral that counteracts unwanted penetration by a male’s corkscrew-shaped penis (a spiral that apparently relaxes when a female solicits copulation). It also has dead-end “pockets” to receive unwanted sperm. An unwanted male may win the battle, but he usually loses the war.

Thus, while some mallard matings may be forced, only a tiny proportion of these matings succeed in producing ducklings. The informed choice of the female prevails. And it is this choice – which delights her eye and, over the generations, that of her ancestors – which has evolved into this extravagant masculine beauty.

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