This activity usually lasts from mid-May until June, but some birds begin building nests as early as March. In southeastern Missouri, broods have been seen as early as April. Females lay an average of about 11 eggs. Both sexes incubate the eggs, and incubation takes 21 to 23 days. The young are black balls of down after hatching, and the adults move them to brood platforms for rearing.
Adults feed the young rails for a few days until they begin foraging on their own.
Still, they may stay with the parents for more than a month. Little is known of the behavior of the birds at this time, but they may be observed occasionally on mud flats pursuing crayfish and other prey. King rails eat a variety of small aquatic animals, and occasionally may consume berries, seeds and other plant foods. Missouri king rails eat mostly crayfish, which need aquatic habitats that are relatively unpolluted. A close relative of the king rail, the clapper rail of coastal salt marshes, shows similar preferences, eating mostly fiddler crabs.