To everyone who is confused about why Pukei-Pukei is a bird wyvern: Usually the build of a monster determines what it is. That is why the Diabolos is a flying Wyvern: He shares anatomic similarities to Rathalos, Legiana and the rest. Pukei-Pukei falls under a different category tho: it is an early game monster. All early game monsters that were winged (usually Yian Kut-Ku or Gypceros in previous games) are also bird wyverns. Also all Raptor-Like Monsters and monsters Related to other bird Wyverns (Yian Garuga) fall under the Bird Wyvern category.