mud is sometimes swallowed and regurgitated prior to use. While nearly all rockfowl nests are found in caves or on cliffs, there are records of nesting occurring on a riverbank and on a fallen tree trunk. Nests are typically constructed at least apart, but one colony had six nests adjoining each other. Nests also vary widely in size, though they average to be long, wide, and deep. It used to be believed that each pair builds two nests, one for breeding and one for roosting; however, recent surveys have found no evidence of this, with all nests in the colony being used for breeding. One to two eggs, typically two, are laid in each nest a day or two apart. The eggs weigh about and have an average size of . The eggs are a creamy white with dark brown blotches spread across the egg but in higher density near the larger end. Incubation, which begins after the first egg is laid, lasts for 23 to 28 days. The parents take turns incubating their eggs. Hatching typically takes at least 12 hours. The infant rockfowl's eyes open after nine to eleven days, while feathers begin to grow seven days after hatching. After the young hatch, food is brought to them almost four times an hour. To feed its young, the adult rockfowl clings to the side of its nest while fluttering its wings; some birds use their tails as a prop underneath the nest to help support themselves. Rockfowl have been known to kill the young of other rockfowl, while nest predation is carried out by cobras of the genus Naja, the Nile monitor, sun squirrels, red-chested goshawks, and Procolobus monkeys. This leads on average to only 0.44 nestlings surviving per pair of rockfowl. Due to potential infanticide by other rockfowl, parents protect their nest and vicious fights often occur. Rare among other bird species, this behaviour is prevalent in white-necked rockfowl. Not fully understood, it is thought to occur for the sake of resource competition or sexual selection. The young leave the nest after 23 to 27 days, at which time they resemble the adult rockfowl but with much shorter tails. The young leave the nest by standing on the edge, emitting a piercing whistle, and then gliding down to the ground on spread wings where they are met by an adult bearing insects. Even after leaving the nest,