Animals that undergo daily torpor include birds (even tiny hummingbirds, notably Cypselomorphae)[1][2] and some mammals, including many marsupial species,[3] rodent species (such as mice), and bats.[4] During the active part of their day, such animals maintain normal body temperature and activity levels, but their metabolic rate and body temperature drops during a portion of the day (usually night) to conserve energy. Torpor is often used to help animals survive during periods of colder temperatures, as it allows them to save the energy that would normally be used to maintain a high body temperature.