It is always exciting to receive a nestling balk eagle to the centre. It's a scenario that gives us mixed feelings - an immense euphoria being so close to this magnificent bird and a sadness that it has been separated from a natural life.
When hatched a nestling is covered with light gray down and is initially wet but dries quickly. Their eyes are brown with pink gape, legs, and skin. They have limited locomotion and when you look at the feet of the nestling you can understand why. The second down begins to emerge at 9–11 days with flight feathers emerging at 2–3 weeks. The body contour feathers begin emerging with the humeral tract at 3–4 weeks. Feathers on its head and back emerge at 4–5 weeks; lateral ventral (underside) surface at 4–6 weeks; and feathering on tarsi (part of the leg of a bird below the thigh) at 6–8 weeks.
Both the male and female parents hunt and feed their young. The adult brings food to nest, tears off small pieces, and delivers them to young at early age. The male provides most of food in first 2 weeks, while the female tends the young in the nest. After 3–4 weeks, the female delivers as much prey as male. Within 3–4 weeks, young able to peck at food but not able to tear off food and will feed self until 6 weeks old.
Daily weight gain is substantial, with maximum average of 102 grams per day. Unbelievably their maximum growth is attained at about 3–4 weeks of age.
When a second chick is hatched in a clutch, signs show a differential growth than the first chick probably due to lack a nutrition. There is continual competition for the food and in some cases fratricide (killing of sibling usually with a boot out of the nest). Mortality is greatest early in the nestling period. If a third egg hatches, the third nestlings rarely receives any food. (Cornell Lab of Ornithology)
Many times, when the nestlings arrive and after a thorough examination by our wildlife staff, the prognosis could be a return to the wild. That is why NIWRA exists and when the day comes for release, we all rejoice.