Diurnal animals are active during daylight hours and rest or sleep at night. Examples include most birds, humans, squirrels, and butterflies. Nocturnal animals are active at night (e.g., owls, bats). Crepuscular animals are active at dawn and dusk (e.g., deer, rabbits). The word 'diurnal' comes from the Latin 'diurnus' meaning 'of the day.'