Well, the chick grew up into a chicken, but you’re still not sure how the egg got into that cave...

Chicka, as she's called for short, is a nasty-tempered hen that hatched from a chicken egg that Ran had sneaked into the home cave in an attempt to obtain her own pet fowl.  She is both willing and able to charge headlong at any dragon eating vegetation, squawking shrilly and pecking relentlessly at their feet until they relinquish their dinner.  As the only creature known to have challenged Preto Osso for his food and not only survive but also win claim, Chicka holds special status in the cave; although she is considered a nuisance, the dragons all view her as an over-dominant 'pet' of sorts and take great care not to step on her as they move about their business.