A species of finch known as the Gouldian Finch can have red, black, or (most rarely) yellow plumage on their heads, and their personalities match their feathers. "Personality" in a biological context refers to consistent behavioral patterns, such as the tendency to be bold or shy across situations.

In this study, researchers found that red-headed finches had a "fiery personality," tending to be more aggressive than their black-headed peers. The black-headed individuals, though, were willing to take more risks with predators, returning to a bird-feeder more quickly than the redheads after a supposed predator sighting (set up by the researchers).

Do redheads and blackheads hang out together? And what drives this correlation: does plumage color influence personality? Or are the two genetically linked? Further research will aim to answer this question.

Even in humans, some physical traits are genetically linked with seemingly complex behavioural or cognitive traits: for example, redheads have greater pain sensitivity and require more anesthesia for surgeries and dental procedures. This peer-reviewed research finding arose from anesthetist urban legends about redheads who would commonly wake up from anesthesia too early. It turns out that your red-headed friend hates the dentist for a reason!

Whether or not blondes have more fun, however, remains to be seen.