The stygian owl is wholly nocturnal. The largest part of its diet is birds, from very small ones to some as large as the 150 g (5.3 oz) lesser nothura (Nothura minor); it is thought that most birds are caught on their nightime roosts. The diet also includes bats (which are seldom preyed on by other owls), some other mammals, frogs, and insects. Also in contrast to other owls, rodents do not appear to be part of its diet