Which action involves taking care of a young bird until it can fly?

The term that specifically refers to the process of a young bird developing its feathers and learning to fly is "fledge." Fledging is a critical developmental stage where a juvenile bird leaves the nest and begins to learn how to fly and fend for itself. This period is essential for the survival of birds, as it involves both physical growth and the acquisition of necessary skills for independence.

In contrast, the other terms do not relate to the care or development of birds. Extradite refers to the formal process of sending an individual back to their home country to face legal issues. Hallow means to honor as holy or greatly revered, and grandstand typically refers to pursuing attention or boasting in a theatrical manner, often in a public context. Thus, "fledge" is the term that appropriately describes the nurturing of a young bird until it achieves the ability to fly.