Vargas (1995) reports that clutch size for the Gray-backed Hawks is one. Eggs are bluish white and are exclusively incubated by the female for 36 days. Fledging occurs 56 to 84 days after hatching (average = 72 days, n = 3). During incubation the male provides food that is supplied to the female on exposed branches away from the nest. At this period birds are very aggressive towards intruders. Nest fidelity seem to be high and birds will tend to reuse their nests in consecutive breeding attempts.
According to Vargas (1995) In Ecuador nests were constructed with branches and lined with green materials. They were located in large trees (average diameter at breast height = 111 cm; n = 10), at heights between 14 and 35 m. Nests were positioned on the main tree ramification (n = 2) or on lateral branches (n = 8), and most were concealed by foliage. 40% of all nests studied in Ecuador were in Ficus sp. trees and most nests (70%) were in forest borders with steep slopes and close to water courses.
Nests dimensions (n = 5 ,Vargas 1995) are:
Greater diameter: 78 m.
Smaller dimeter: 54 cm.
Height: 37 cm.
Cup depth: 14 cm.