Editing Hibernation (section)

==Dormancy and freezing in ectotherms==
{{Main|Cryopreservation#Freeze tolerance in animals}}
Because they cannot actively down-regulate their body temperature or metabolic rate, [[Ectotherm|ectothermic animals]] (including fish, reptiles, and amphibians) cannot engage in obligate or facultative hibernation. They can experience decreased metabolic rates associated with colder environments or low oxygen availability ([[Hypoxia (medical)|hypoxia]]) and exhibit dormancy (known as brumation). It was once thought that [[basking shark]]s settled to the floor of the [[North Sea]] and became dormant, but research by David Sims in 2003 dispelled this hypothesis,<ref>{{cite journal|title=Seasonal movements and behavior of basking sharks from archival tagging|journal=Marine Ecology Progress Series|volume=248|pages=187–196|year=2003|doi=10.3354/meps248187|url=https://www.int-res.com/articles/meps2003/248/m248p187.pdf|last1=Sims|first1=DW|last2=Southall|first2=EJ|last3=Richardson|first3=AJ|last4=Reid|first4=PC|last5=Metcalfe|first5=JD|doi-access=free}}</ref> showing that the sharks traveled long distances throughout the seasons, tracking the areas with the highest quantity of [[plankton]]. [[Epaulette shark]]s have been documented to be able to survive for three hours without oxygen and at temperatures of up to {{convert|26|C|F}}<ref>{{cite journal|title=A Shark With an Amazing Party Trick|journal=New Scientist|volume=177|issue=2385|pages=46|date=8 March 2003|url=http://www.flmnh.ufl.edu/fish/sharks/innews/sharktrick2003.htm|archive-url=https://web.archive.org/web/20030426034734/http://www.flmnh.ufl.edu/fish/Sharks/InNews/sharktrick2003.htm|url-status=dead|archive-date=26 April 2003|access-date=2006-10-06}}</ref> as a means to survive in their shoreline habitat, where water and oxygen levels vary with the tide. Other animals able to survive long periods with very little or no oxygen include [[goldfish]], [[red-eared slider]]s, [[wood frog]]s, and [[bar-headed goose|bar-headed geese]].<ref>{{Cite magazine|url=http://www.papimi.gr/breathless.htm|title=Breathless: A shark with an amazing party trick is teaching doctors how to protect the brains of stroke patients|author=Douglas Fox|magazine=[[New Scientist]]|volume=177|issue=2385|date=March 8, 2003|page=46|access-date=November 9, 2006|archive-date=February 29, 2012|archive-url=https://web.archive.org/web/20120229221148/http://www.papimi.gr/breathless.htm|url-status=dead}}</ref> The ability to survive hypoxic or anoxic conditions is not closely related to endotherm hibernation.

Some animals can literally survive winter by freezing. For example, some [[fish]], [[amphibian]]s, and [[reptile]]s can naturally freeze and then "wake" up in the spring. These species have evolved freeze tolerance mechanism such as [[antifreeze protein]]s.<ref>{{Cite book|last1=Vitt|first1=Laurie J.|last2=Caldwell|first2=Janalee|url=https://www.worldcat.org/oclc/839312807|title=Herpetology: an introductory biology of amphibians and reptiles|year=2014|isbn=978-0-12-386919-7|edition=4th|location=Amsterdam|oclc=839312807}}</ref>