A nestling is a young bird that has not yet developed feathers and is typically unable to leave the nest. These birds are usually dependent on their parents for food and protection. Nestlings are often found in the nests of their parents, where they receive care until they are ready to fledge, or leave the nest. During the nestling stage, birds undergo significant growth and development. They are fed a diet rich in protein, which helps them grow strong enough to eventually fly. Common examples of nestlings include species like sparrows, robins, and blue jays, all of which require parental care during this vulnerable period.