When does a young bird achieve the stage known as fledge?

A young bird reaches the fledge stage when it leaves the nest. This stage is crucial in a bird's development, marking the transition from being dependent on parents for warmth and food to achieving a level of independence. Fledging typically occurs after the bird has developed enough strength and coordination in its wings to take its first flight.

While learning to fly, building a nest, and starting to feed itself are important milestones in a bird's life, they either occur before or are part of the process leading up to fledging. The act of leaving the nest indicates not just physical readiness to fly but also developing the skills necessary for survival outside the nest environment. Thus, leaving the nest is the definitive moment that signifies a young bird has fledged.