Editing Hibernation (section)

===Obligate hibernation===
[[File:Marmota monax UL 07.jpg|thumb|[[Groundhog]] gathering [[Nesting instinct|nesting]] material for its warm [[burrow]] in preparation for hibernation]]
Obligate hibernators are animals that spontaneously, and annually, enter hibernation regardless of ambient temperature and access to food. Obligate hibernators include many species of [[ground squirrel]]s, other [[rodents]], [[European hedgehog]]s and other [[insectivores]], [[monotremes]], and [[marsupials]].{{citation needed|date=December 2022}} These species undergo what has been traditionally called "hibernation": a physiological state wherein the body temperature drops to near ambient temperature, and heart and respiration rates slow drastically.

The typical winter season for obligate hibernators is characterized by periods of [[torpor]] interrupted by periodic, euthermic arousals, during which body temperatures and heart rates are restored to more typical levels. The cause and purpose of these arousals are still not clear; the question of why hibernators may return periodically to normal body temperatures has plagued researchers for decades, and while there is still no clear-cut explanation, there are multiple hypotheses on the topic. One favored hypothesis is that hibernators build a "[[sleep debt]]" during hibernation, and so must occasionally warm up to sleep. This has been supported by evidence in the [[Arctic ground squirrel]].<ref>{{cite journal |vauthors=Dan S, Barnes BM, Strijkstra AM |title=Warming up for sleep? Ground squirrels sleep during arousals from hibernation |journal=Neuroscience Letters |volume=128 |issue=2 |pages=265–268 |year=1991 |pmid=1945046 |doi=10.1016/0304-3940(91)90276-Y |s2cid=13802495 |url=https://www.rug.nl/research/portal/en/publications/warming-up-for-sleep--ground-squirrels-sleep-during-arousals-from-hibernation(a2c377a6-7cf9-4fd1-bebd-5cca8583762a).html |access-date=2019-12-05 |archive-date=2020-09-28 |archive-url=https://web.archive.org/web/20200928004231/https://www.rug.nl/research/portal/en/publications/warming-up-for-sleep--ground-squirrels-sleep-during-arousals-from-hibernation(a2c377a6-7cf9-4fd1-bebd-5cca8583762a).html |url-status=dead }}</ref> Other theories postulate that brief periods of high body temperature during hibernation allow the animal to restore its available energy sources<ref>{{cite journal |last=Galster |first=W. |author2=Morrison, P. R. |title=Gluconeogenesis in arctic ground squirrels between periods of hibernation |journal= American Journal of Physiology. Legacy Content|year=1975 |volume=228 |issue=1 |pages=325–330 |pmid=1147024 |doi=10.1152/ajplegacy.1975.228.1.325 |s2cid=1125482 }}</ref> or to initiate an immune response.<ref>{{cite journal |author1=Prendergast, B.J. |author2=Freeman, D.A. |author3=Zucker, I. |author4=Nelson, R.J. |title=Periodic arousal from hibernation is necessary for initiation of immune responses in ground squirrels |journal= American Journal of Physiology. Regulatory, Integrative and Comparative Physiology|year=2002 |volume=282 |issue=4 |pages=R1054–R1062 |doi=10.1152/ajpregu.00562.2001 |pmid=11893609|s2cid=8967165 }}</ref>

Hibernating Arctic ground squirrels may exhibit abdominal temperatures as low as {{convert|−2.9|C|F}}, maintaining sub-zero abdominal temperatures for more than three weeks at a time, although the temperatures at the head and neck remain at {{convert|0|C|F}} or above.<ref>{{cite journal |last=Barnes |first=Brian M. |date=30 June 1989 |title=Freeze Avoidance in a Mammal: Body Temperatures Below 0&nbsp;°C in an Arctic Hibernator |journal=Science |volume=244 |pages=1593–1595 |url=http://users.iab.uaf.edu/~brian_barnes/publications/1989barnes.pdf |access-date=2008-11-23 |doi=10.1126/science.2740905 |pmid=2740905 |issue=4912 |url-status=dead |archive-url=https://web.archive.org/web/20081216233837/http://users.iab.uaf.edu/~brian_barnes/publications/1989barnes.pdf |archive-date=16 December 2008 |df=dmy-all |bibcode=1989Sci...244.1593B}}</ref>