These sites provide sufficient food for raising young. Like other North American rails, adult king rails molt their flight feathers after the young become independent. Once they grow new flight feathers, adults apparently leave Missouri for southern wintering areas. This occurs mostly in September, but they have been observed in Missouri through late October. Because king rails are found more often by sound than by sight, population monitoring is based on listening.
Rails respond vocally to taped calls.
Such methods have been used in Missouri to determine where king rails live during the breeding season, but otherwise we know little about their populations and what causes them to vary. Healthy habitats usually support good populations, but good king rail habitat is rare nowadays in Missouri. Today, king rails are considered endangered as a breeding species in Missouri. Their biggest threat is the loss of high-quality wetlands. Such wetlands are vulnerable to drainage and drought, as well as to deep flooding during heavy rainfall.