A patch over a male Gouldian finch’s right eye works like beer goggles, though the bird doesn’t need booze to flirt unwisely. If limited to using his left eye when checking out possible mates, he risks making really stupid choices.
Gouldian finches have caps of black, red or yellow feathers on their heads. In nature, the birds prefer to mate with partners with the same cap color. Yet black-headed males rendered temporarily left-eyed by a tiny removable eye patch flirted as readily with red-heads as with black-heads, says cognitive ecologist Jennifer Templeton of Knox College in Galesburg, Ill. That’s not smart because daughters typically fail to survive when Gouldian finches mate outside their cap color.
Also the male himself “becomes less attractive,” Templeton says. When the bird’s right eye was covered, he sang, bowed and posed less during his attempts at courtship. Some left-eyed males didn’t manage to make up their minds at all, but “just hopped around randomly,” Templeton says.
Moving the eye patch to uncover the right eye and block the left, however, restored male Gouldian finches to their senses. Males then spent more time perching near same-cap-color females and flirting with them. “Beauty is in the right eye of the beholder,” Templeton and her colleagues conclude online October 3 in Biology Letters.
Birds make fine subjects for comparing eye biases because many species’ eyes sit on opposite sides of their skulls with very different fields of view. A bird’s right eye connects to the left hemisphere of its brain, and the left eye to the right hemisphere. Unlike mammals, birds don’t have a high-speed connection between hemispheres. (A bird’s neural structure does allow information to transfer, but it takes hours.) So detecting an eye bias in birds gives clues to what goes on in their brains.
The importance of the right eye/left brain for flirting among these finches and other birds might at first seem to contradict another long-standing finding of mating bias, says Lesley Rogers of the University of New England in Armidale, Australia. It’s the other, right hemisphere, that controls copulation, she says. “Yet in order to view a mate it is necessary to suppress copulation, at least initially.”
Specialization in one hemisphere has turned up in lizards, fish and birds for a wide range of tasks. An intruder may get attacked more readily if approaching on one side versus the other. And one hemisphere may be more specialized for distinguishing an animal’s own species from others, a vital step in choosing a mate. Earlier studies have already noted brain-side biases in mate choice. Zebra finches, for example, tend to stare at the object of their desire with the right eye rather than the left.