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Go to CuriosityStream.com/SciShow to learn more. [♪ INTRO]. On the remote, rocky islands of the North Pacific, you might find a happy-looking little bird.

Called the crested auklet, it looks kind of like a cross between a penguin and a quail. They live in big, dense, noisy colonies and go out to the ocean to feed. They also, apparently, smell like tangerines.

The smell, which has been described as “distinctive” and “pungent”, emerges at the beginning of the breeding season. As for what's actually causing it, the smell seems to come from a mix of compounds secreted by a patch of special, hair-like, possibly hollow feathers called wick feathers found on a particular area of skin on their back. They just got a little tangerine patch back there.

The mix of compounds is dominated by aldehydes, a kind of chemical that contains a carbon bonded to a hydrogen and double-bonded to an oxygen. As for why, there are two hypotheses. One is that the smelly aldehydes might be a way for the birds to repel parasites like lice — kind of like a built-in can of bug spray.

Experiments have shown that some of the compounds in the smell can repel or paralyze ticks or lice. The other idea is that it might be some kind of sexual display or some other sort of social signal. During courtship, crested auklets approach potential mates and bury their bill in that patch in what's known as a “ruff-sniff”.

And they can definitely smell it. Studies have shown the birds can tell the scent apart from other smells and even appeared to be attracted to it when presented with a smelly fake bird. Which is kind of neat, because for a long time many experts thought birds couldn't really smell things.

That idea was debunked by scientists in the 1960's, and that research doesn't have much of anything to do with crested auklets, but as a myth it's had surprising staying power. It might seem kind of funny, but choosing the smelliest mate might have some benefits. If the scent is a parasite repellent, for example, a smelly mate is less likely to pass infestations to their mate or offspring.

The smell might also be an indicator of how healthy the animal is in general. Its body has to produce those smelly chemicals, which requires energy. And because all smells eventually fade over time, an animal that depends on cologne to win a mate has to keep making new compounds all the time.

Which means it has the energy to burn to make smelly molecules, even though those resources could be used for other, more survival-oriented things. This means for crested auklets, a strong scent might be a way to show that you're not only healthy, but you have the resources to burn. Citrus-scented birds are pretty neat, but they're far from the only fascinating animals out there.

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