For king penguins, there may be nothing sexier than a nice beak. The species, one of the biggest of the penguins, come onshore to find mates and breed in large colonies, and are monogamous throughout a single breeding season. A new study finds that the success of their efforts to woo fellow penguins depends largely on one quality: the color of their beaks.

King penguins have blotches of orange on the bottom of their beaks that might help them find a romantic match, a study in the journal Ethology reports. Penguins can see in ultraviolet, and to them these beak spots are even more colorful than the limited orange hue humans can see. In studying a group of some 200,000 penguins who came to breed on the Kerguelen Islands in the southern Indian Ocean (somewhat near the midpoint between Africa, Australia, and Antarctica), researchers from the French Centre d’Ecologie Fonctionnelle et Evolutive found that flirting penguins were more likely to form lasting pairs for the season if their beak colors were the same. 

The scientists studied 75 pairs of penguins who were still in the speculative phase of their courtship. Some of those penguins would stay together and lay eggs, while others would eventually move on to other potential mates. They found that no other penguin ornamentation had an effect on whether or not the penguin pairs would stay together except beak color. Breast feathers and other spots of elaborate color did not draw mates, but the penguins who formed committed relationships tended to have the same beak spot colors (even accounting for the differences between human and penguin vision). 

For penguins, it seems, compatibility is all about the beak. 

[h/t: Discover]