Male fish in the Colorado River roll their eyes to flash a novel "Back off, punk" signal at other males, researchers say.
The razorback suckers' gesture—dipping the eyeball to expose its upper third—ranks as the first documented eye roll among territorial signals, says vision specialist Inigo Novales Flamarique of Simon Fraser University in Burnaby, British Columbia. What makes the communication even more unusual, he says, is that it gets much of its punch from ultraviolet (UV) light.
People don't see UV wavelengths, but biologists have in recent years found that certain fish, birds, and other animals do.
Flamarique had puzzled over the UV vision in a razorback relat