While the good-looking, dulcet-toned Ryan Goslings of this world are a rare breed, it seems for real-life goslings, this magic combo is even harder to find. According to a new study, ladies in the avian world have to settle for either dashing looks or a beautiful voice in their prospective partners, they can’t have both.
Male birds often rely on song or appearance to woo potential mates. Birds of paradise use their ridiculously lavish hairdos to draw in females, while the nightingale uses its incredible song. But while the aptly named emperor bird of paradise, splendid astrapia, and long-wattled umbrellabird look pretty sexy, they aren’t as tuneful as the nightingale, a decidedly drab-looking pale-brown bird.
The complex song of the nightingale.
There appears to be a trade-off between looks and musicality, and that’s exactly what University of Sheffield researcher Christopher Cooney and his colleagues found in a study recently published in Royal Society Proceedings B.
The team analyzed the songs of 518 bird species, and then quantified how colorful their plumage was. They also looked at how plumage differed between males and females of the same species.
A greater difference between the sexes suggests that the males’ lavish looks have evolved solely to impress. This is known as sexual selection, a kind of natural selection that involves certain traits of one sex evolving because they are favored by the other. This is particularly evident in birds – think male and female peacocks – but can be seen throughout the animal kingdom. Moose with the biggest antlers, elephant seals with the most strength, and lions with the darkest manes all receive the most attention.
The researchers found that the species in which the males had fancier plumage than the females tended to have duller songs than species where the males and females looked more alike.
So why would males settle for one or the other, rather than being talented songsters while also looking good? One key explanation is that it is costlier to develop both traits, but there are several other possibilities too.
“One idea is that such a trade-off could be driven by habitat differences among species, with plumage ornamentation favored in one habitat type (eg light, open habitats) and complex song favored in others (e.g. dark, dense forest),” Cooney told IFLScience. “However, we were able to test this hypothesis and found no evidence for this effect.
“Another alternative explanation is simply that when one signal type (either plumage or song) becomes exaggerated first, the other type of signal becomes 'redundant', as it pays to pay attention to the signal type that is most attractive or carries the most information.”
Cooney noted that more research is needed to find out which is responsible. What’s more, as with all things, there are exceptions to the rule.
“Perhaps one of the most famous examples of a bird species with exaggerated plumage and song is the superb lyrebird (Menura novaehollandiae),” Cooney told IFLScience. “The males of this species have extravagant tail ornaments and a complex vocal display, including an extraordinary ability to mimic the sounds of other birds. Such 'exceptions to the rule' are fascinating, as they can reveal a lot about the underlying factors that favor the evolution of complex plumage patterns or song – or both in some cases.”
The superb lyrebird doing its thing.