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Aestivation or æstivation (from Latin aestas, summer, but also spelled "estivation" in American English) is a state of animal dormancy, similar to hibernation, characterized by inactivity and a lowered metabolic rate, that is entered in response to high temperatures and arid conditions. It takes place during times of heat and dryness, the hot dry season, which are often the summer months.
Invertebrate and vertebrate animals are known to enter this state to avoid damage from high temperatures and the risk of desiccation. Both terrestrial and aquatic animals undergo aestivation.
Gastropoda: Some air-breathing land snails, including species in the genera Helix, Cernuella, Theba, Helicella, Achatina and Otala, commonly aestivate during periods of heat. Some species move into shaded vegetation or rubble. Others climb up tall plants, including crop species as well as bushes and trees, and will also climb man-made structures such as posts, fences, etc.
The habit of climbing vegetation to aestivate has caused more than one introduced snail species to be declared an agricultural nuisance.
To seal the opening to their shell to prevent water loss, pulmonate land snails secrete a membrane of dried mucus called an epiphragm. In certain species, such as Helix pomatia, this barrier is reinforced with calcium carbonate, and thus it superficially resembles an operculum, except that it has a tiny hole to allow some oxygen exchange.
Reptiles and amphibians 
Non-mammalian animals that aestivate include North American desert tortoises, crocodiles, and salamanders. Some amphibians (e.g. the cane toad and greater siren) aestivate during the hot dry season by moving underground where it is cooler and more humid. The California red-legged frog may aestivate to conserve energy when its food and water supply is low.
The Water-holding Frog has an aestivation cycle. It buries itself in sandy ground in a secreted, water-tight mucus cocoon during periods of hot, dry weather. Australian Aborigines discovered a means to take advantage of this by digging up one of these frogs and squeezing it, causing the frog to empty its bladder. This dilute urine--up to half a glassful--can be drunk. However, this will cause the death of the frog which will be unable to survive until the next rainy season without the water it had stored.
Although relatively uncommon, a small number of mammals aestivate. Animal physiologist Kathrin Dausmann of Philipps University of Marburg, Germany, and coworkers presented evidence in a 2004 edition of Nature that the Malagasy fat-tailed dwarf lemur hibernates or aestivates in a small tree hole for seven months of the year. According to the Oakland Zoo in California, East African Hedgehogs are thought to aestivate during the dry season.
See also 
- William Charles Miller (2007). Trace Fossils: Concepts, Problems, Prospects. Elsevier. p. 206. ISBN 978-0-444-52949-7.
- Philip Withers, Scott Pedler & Michael Guppy (1997). "Physiological adjustments during aestivation by the Australian land snail Rhagada tescorum (Mollusca: Pulmonata: Camaenidae)". Australian Journal of Zoology 45 (6): 599–611. doi:10.1071/ZO97009.
- Kenneth S. Hagen (1962). "Biology and ecology of predaceous Coccinellidae". Annual Review of Entomology 7: 289–326. doi:10.1146/annurev.en.07.010162.001445.
- Charlwood, JD , Vij, R , Billingsley, PF (2000). "Dry season refugia of malaria-transmitting mosquitoes in a dry savannah zone of east Africa". American Journal of Tropical Medicine and Hygiene 62 (6): 726–732.
- Bob Moore (September 29, 2009). "Estivation: The Survial Siesta". Audubon Guides. Retrieved September 5, 2012.
- |author=F. H. Pough, R. M. Andrews, J. E. Cadle, M. L. Crump, A. H. Savitzky & K. D. Wells |year=2001 |title= Herpetology, second edition |publisher= Prentice Hall |place of publication=Upper Saddle River, New Jersey.
- R. G. Delaney, S. Lahiri & A. P. Fishman (1974). "Aestivation of the African lungfish Protopterus aethiopicus: cardiovascular and respiratory functions" (PDF). Journal of Experimental Biology 61 (1): 111–128.
- A. P. Fishman, R. J. Galante, A. Winokur & A. I. Pack (1992). "Estivation in the African lungfish". Proceedings of the American Philosophical Society 136 (1): 61–72. JSTOR 986798.
- McNab, Brian Keith (2002). The physiological ecology of vertebrates: a view from energetics. Cornell University Press. p. 388. ISBN 978-0-8014-3913-1.
- Kathrin H. Dausmann, Julian Glos, Jörg U. Ganzhorn & Gerhard Heldmaier (2004). "Physiology: hibernation in a tropical primate". Nature 429 (6994): 825–826. doi:10.1038/429825a. PMID 15215852.
- "East African Hedgehog". Oakland Zoo. Retrieved September 5, 2012.
Further reading 
- Navas, Carlos Arturo & Carvalho, José Eduardo (2009). Aestivation: Molecular and Physiological Aspects. Springer. ISBN 978-3-642-02420-7.
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