Distributional records of hoary bats, Lasiurus cinereus Peale and Beauvois, were assembled and mapped for each month. In North America females are seen to migrate northward somewhat earlier than males and to occupy an eastern summering ground where young are born, while males are concentrated in western North America. Fall migration begins in August. Spring and fall migratory waves have been noted, some segregated as to sex. Some South American hoary bats migrate, while others may be non-migratory.