The progression of the beak over time from its initial formation until its mature state. The avian beak is an external anatomical structure, in the head region, that is adapted for feeding self and young, catching prey, probing, etc. It encompasses, but is not restricted to, the maxilla, mandible, maxillary rhamphotheca, mandibular rhamphotheca, nostril, nasal fossa, nasal bones, egg tooth and rictus.