The first egg hatches after 31 to 36 days of incubation. The eggs hatch successively; although the average interval between egg-laying is 3 days, the young tend to hatch no more than a day or two apart. Like all owls that nest in the open, the downy young are often a mottled grey with some white and buff, which provides camouflage. They open their eyes at 4 days of age. The chicks grow rapidly, being able to consume small prey whole after roughly 3 weeks. In Andalusia, the most noticeable development of the young before they leave the nest was the increase of body size, which was the highest growth rate of any studied owl and faster than either snowy or great horned owls. Body mass increased fourteen times over from 5 days old to 60 days old in this study. The male continues to bring prey, leaving it on or around the nest, and the female feeds the nestlings, tearing up the food into suitably sized pieces. The female resumes hunting after about 3 weeks, which increases the food supply to the chicks. Siblicide has been recorded widely in Eurasian eagle-owls, and according to some authorities, is almost a rule in the species. Many nesting attempts produce two fledglings, indicating that siblicide is not as common as in other birds of prey, especially some eagles. In Spain, males are thought to be the first egg laid to reduce the likelihood of sibling aggression due to the size difference, thus the younger female hatchling is less likely to be killed, since it is similar in size to its older sibling.