Aren't you glad this is a bird study?

Male great tits with brighter breasts have stronger sperm, according to the first study to find a link between flashiness and sperm strength. The birds' vibrant plumage appears to act like a flashing billboard, broadcasting the males' reproductive superiority to females eager to produce offspring.

The advertisement likely finds an appreciative audience in female great tits, since snagging a male with high-quality sperm isn't exactly a lark. That's in part because free radicals threaten sperm cells in many animals, including humans. Created by cells when stressed by pollution and other factors, free radicals are groups of oxygen-activated atoms that can damage sperm cells, weakening their swimming ability.

Many animals' bodies produce antioxidants that fight free radicals—including male great tits. The birds have an antioxidant called carotenoid that not only defends against free radicals but also gives their breast feathers a yellow hue. The new research shows that in males with more carotenoid, and thus more color, the sperm is better able to withstand a free radical onslaught—and females seem to know it.

Though human males don't display ornate natural plumage, the bird research has some parallels to people, said study leader Fabrice Helfenstein, an evolutionary ecologist at the University of Bern in Switzerland. For instance, free radicals are thought to be a major cause of infertility in people. Likewise, some studies have shown that men with more attractive faces have better quality semen.

Read more at National Geographic.