Editing Reindeer (section)

=== Social structure, migration and range ===
[[File:Caribou using antlers.jpg|thumb|The size of the antlers plays a significant role in establishing the hierarchy in the herd.<ref name=walker/>]]
Some populations of North American caribou; for example, many herds in the barren-ground caribou subspecies and some woodland caribou in [[District of Ungava|Ungava]] and northern [[Labrador]], [[Animal migration|migrate]] the farthest of any terrestrial mammal, traveling up to {{cvt|5000|km|-3}} a year, and covering {{cvt|1000000|km2|-5}}.<ref name="iucn status 19 November 2021" /><ref>[http://www.mrnf.gouv.qc.ca/english/wildlife/maps-caribou/ Caribou Migration Monitoring by Satellite Telemetry] {{webarchive|url=https://web.archive.org/web/20120514111934/http://www.mrnf.gouv.qc.ca/english/wildlife/maps-caribou/ |date=14 May 2012 }}. Mrnf.gouv.qc.ca. Retrieved on 16 September 2011.</ref> Other North American populations, the boreal woodland caribou for example, are largely sedentary.<ref name=Bergerud>{{Cite journal
| pmid = 21227095
| year = 1988
| last1 = Bergerud
| first1 = A. T.
| title = Caribou, wolves and man
| journal = Trends in Ecology & Evolution
| volume = 3
| issue = 3
| pages = 68–72
| doi = 10.1016/0169-5347(88)90019-5
| bibcode = 1988TEcoE...3...68B
}}</ref> The European populations are known to have shorter migrations. Island populations, such as the Novaya Zemlya and Svalbard reindeer and the Peary caribou, make local movements both within and among islands. Migrating reindeer can be negatively affected by [[Parasitism|parasite]] loads. Severely infected individuals are weak and probably have shortened lifespans, but parasite levels vary between populations. Infections create an effect known as [[culling]]: infected migrating animals are less likely to complete the migration.<ref name="Bartel Ober">{{cite journal|last1=Bartel|first1=Rebecca|last2=Oberhauser|first2=Karen |author-link2=Karen Oberhauser |last3=De Roode|first3=Jacob|last4=Atizer|first4=Sonya |title=Monarch butterfly migration and parasite transmission in eastern North America|journal=Ecology|date=February 2011|volume=92|issue=2 |pages=342–351|doi=10.1890/10-0489.1|pmid=21618914|pmc=7163749|bibcode=2011Ecol...92..342B |s2cid=9018584}}</ref>

Normally travelling about {{cvt|19|-|55|km}} a day while migrating, the caribou can run at speeds of {{cvt|60|-|80|km/h}}.<ref name="iucn status 19 November 2021" /> Young calves can already outrun an Olympic sprinter when only 1 day old.<ref name="Hoare 2009 45">{{cite book|last=Hoare|first=Ben|title=Animal Migration|year=2009|publisher=Natural History Museum|location=London |isbn=978-0-565-09243-6|page=45}}</ref> During the spring migration, smaller herds will group together to form larger herds of 50,000 to 500,000 animals, but during autumn migrations, the groups become smaller and the reindeer begin to mate. During winter, reindeer travel to forested areas to forage under the snow. By spring, groups leave their winter grounds to go to the calving grounds. A reindeer can swim easily and quickly, normally at about {{cvt|6.5|km/h}} but, if necessary, at {{cvt|10|km/h}} and migrating herds will not hesitate to swim across a large lake or broad river.<ref name="iucn status 19 November 2021" />

The barren-ground caribou form large herds and undertake lengthy seasonal migrations from winter feeding grounds in taiga to spring calving grounds and summer range in the tundra. The migrations of the [[Porcupine caribou|Porcupine]] herd of barren-ground caribou are among the longest of any mammal.<ref name="Eder2011" /> Greenland caribou, found in southwestern [[Greenland]], are "mixed migrators" and many individuals do not migrate; those that do migrate less than 60&nbsp;km.<ref>Raundrup, K. (2018) Movement patterns and resource selection - insights from West Greenland caribou. PhD Thesis, Denmark: Aarhus University, 115 pp.</ref> Unlike the individual-tending mating system, aggregated rutting, synchronized calving and aggregated post-calving of barren-ground caribou, Greenland caribou have a harem-defense mating system and dispersed calving and they do not aggregate.<ref name=Poole/>

Although most wild tundra reindeer migrate between their winter range in taiga and summer range in tundra, some ecotypes or herds are more or less sedentary. Novaya Zemlya reindeer (''R. t. pearsoni'') formerly wintered on the mainland and migrated across the ice to the islands for summer, but only a few now migrate.<ref name="Mizin-2018a">{{Cite journal |last1=Mizin |first1=Ivan A. |last2=Sipko |first2=Taras P. |last3=Davydov |first3=Andrey V. |last4=Gruzdev |first4=Alexander R. |date=2018 |title=The wild reindeer (''Rangifer tarandus'': Cervidae, Mammalia) on the arctic islands of Russia: a review |journal=[[Nature Conservation Research]] |volume=3 |issue=3 |doi=10.24189/ncr.2018.040 |issn=2500-008X|doi-access=free }}</ref> Finnish forest reindeer (''R. t. fennicus'') were formerly distributed in most of the coniferous forest zones south of the tree line, including some mountains, but are now spottily distributed within this zone.

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As an adaptation to their Arctic environment, they have lost their [[circadian rhythm]].<ref>[https://www.wired.com/wiredscience/2010/03/arctic-reindeer-circadian-clock/ Arctic Reindeer Go Off the Circadian Clock] {{webarchive|url=https://web.archive.org/web/20131220020321/http://www.wired.com/wiredscience/2010/03/arctic-reindeer-circadian-clock/ |date=20 December 2013 }}. Wired.com (3 April 2014). Retrieved on 19 April 2014.</ref>

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