Which characteristic defines altricial birds upon hatching?

Altricial birds are defined by their state upon hatching, which is characterized by being blind and helpless. This means that they are born in a very undeveloped stage, requiring substantial parental care for survival. Unlike precocial birds, which are often able to walk and feed themselves shortly after hatching, altricial birds depend on their parents for warmth, food, and protection during the early stages of their life. Their eyes are usually closed at birth, and they lack feathers, which makes them vulnerable in their environment.

The other characteristics mentioned in the options refer to different types of birds or developmental strategies. For instance, the ability to fly immediately is a trait of precocial birds, which are born more developed. Feathered birds would typically not be categorized as altricial at hatching, since feather development comes after a period of growth, and independent feeding is not a characteristic of altricial species; they rely completely on their parents until they develop the necessary skills for self-sufficiency.