The most recent assessments indicate that the Caribbean manatee (T. manatus), Amazonian manatee (T. inunguis) and dugong (Dugong dugon) breed continuously (Anderson and Heinsohn 1978; Hartman 1971; Husar 1975, 1977a, 1977b; Pereira 1945). Little is known of the reproductive biology of the Senegal manatee (T. senegalensis). This note presents evidence that the Amazonian manatee is a seasonal breeder with a prolonged calving period.