Fledge is the stage in a young bird's life when the feathers and wing muscles are sufficiently developed for flight. It also describes the act of raising chicks to a fully grown state by the chick's parents.

In ornithology, the meaning of fledging is variable, depending on species. Birds are sometimes considered fledged once they leave the nest, even if they still can't fly. Some definitions of fledge take it to mean the independence of the chick from the adults, as adults will often continue to feed the chick after it has left the nest and is able to fly.

One notable species, the Ancient Murrelet, fledges two days after hatching, running from its burrow to the ocean and its calling parents. Once it reaches the ocean it is cared for several weeks by its parents. Other species, such as Guillemots and some cormorants leave the nesting site before they are able to fly, or barely able to fly. The fledging behaviour of the guillemot is spectacular; the adult will lead the chick through the colony if possible, for large drops like cliffs, it will fly down and call to its young. The chick will then launch itself off the cliff, attempting to fly as far as possible, crash landing on the ground below before continuing its run towards the ocean.