When you look at a rockhopper penguin, the first things you probably notice are its yellow crests - a trait they share with other crested penguins, like Macaroni and Snare's penguins. Clearly, having a fly hairstyle matters in the penguin world -but why?
Juvenile penguins don't have crests
Juvenile penguins are often the same size as adults - so they need some way of signalling that they are not competition for mates while trying to find their place in the colony. Some species, like African penguins, are a completely different colour while juvenile, but crested penguins are the same colour as the adults when young - just missing their crests.
It helps them hunt
Rockhopper penguins often share island habitats with other penguin species, like gentoos or king penguins. Crested-penguins, like rockhoppers, are able to see each other's yellow crests underwater, helping them differentiate between members of their species and "the competition" when coordinating hunting.
It's sexy and they know it
They wave their hair like they just don't care! When calling to attract mates, rockhoppers shake their heads - longer, yellower crests signal to other single penguins that a potential mate is mature and healthy.
Bonus fact: Most birds that have yellow colour get the yellow pigment from their food. For example, canaries are yellow because they eat insects that contain carotenoids. Crested penguins have a unique yellow pigment which does not occur anywhere else in nature - which means they make their yellow all by themselves!