Flashy tits equals stronger sperm–at least in the bird world.

A recent study of the birds known as great tits, by evolutionary ecologist Fabrice Helfenstein at the University of Bern, Switzerland, found that the more colorful and bright a male tit’s plumage, the stronger the bird’s sperm is.

The study, published in Ecology Letters, explains that the plumage of some birds contains caretenoids–important antioxidants that can help the bird combat cellular damage caused by stress from predators or feeding babies. A higher amount of caretenoids also results in intensely colored plumage in males, signaling the bird’s increased capacity to ward off stress and preserve its sperm from damage.

New Scientist reports:

[Fabrice Helfenstein] tested this by upping the parental workload of wild male great tits, Parus major – which have yellow breast plumage – by adding two extra chicks to their nests. After five days of looking after their big brood, males with paler plumage suffered a greater reduction in sperm motility than more colorful males. Supplementing the birds’ diet with carotenoids markedly improved the sperm quality of the paler males.

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