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Estivation or aestivation (from Latin aestas, summer) is a rare state of dormancy similar to hibernation, but during the months of the summer. Animals that estivate spend a summer inactive and insulated against heat to avoid the potentially harmful effects of the season (such as the increase in temperature, or relative lack of water), or to avoid contact with other species with which they may otherwise be in competition, or for which they are prey. Some animals, including the California red-legged frog, may estivate to conserve energy when their food and water supply is low.Both land-dwelling and aquatic animals undergo estivation. Animals that estivate include North American desert tortoises, crocodiles, salamanders, and lungfishes. The lungfish estivates by burying itself in mud formed at the surface of a dried up lake. In this state, the lungfish can survive for many years. Other animals estivate in their burrow and wait for autumn to come.Snails also estivate during periods of heat during the day. They move into the vegetation, away from the ground heat, and secrete a membrane made of calcium over the opening to their shell in order to prevent water loss.Until recently no primate, and no tropical mammal, was known to estivate. However, animal physiologist Kathrin Dausmann of Philipps University of Marburg, Germany, and coworkers presented evidence in the 24 June 2004 edition of Nature that the Madagascan fat-tailed dwarf lemur hibernates or estivates in a small cricket hollow for seven months of the year.