Editing Reindeer (section)

== Biology and behaviors ==
=== Seasonal body composition ===
[[File:Svensk ren.JPG|thumb|Sweden]]

Reindeer have developed adaptations for optimal metabolic efficiency during warm months as well as for during cold months.<ref>Karasov, W.H. and Martinez del Rio, C. 2007. ''The Chemistry and Biology of Food in Physiological Ecology: How Animals Process Energy, Nutrients, and Toxins'' (pp. 49–108).</ref> The body composition of reindeer varies highly with the seasons. Of particular interest is the body composition and diet of breeding and non-breeding females between the seasons. Breeding females have more body mass than non-breeding females between the months of March and September with a difference of around {{cvt|10|kg}} more than non-breeding females. From November to December, non-breeding females have more body mass than breeding females, as non-breeding females are able to focus their energies towards storage during colder months rather than lactation and reproduction. Body masses of both breeding and non-breeding females peaks in September. During the months of March through April, breeding females have more fat mass than the non-breeding females with a difference of almost {{cvt|3|kg}}. After this, however, non-breeding females on average have a higher body fat mass than do breeding females.<ref name="Chan-McLeod AC 1999">{{cite journal | last1 = Allaye Chan-McLeod | first1 = A.C. | last2 = White | first2 = R.G. | last3 = Russell | first3 = D.E. | year = 1999 | title = Comparative body composition strategies of breeding and nonbreeding female caribou | journal = Canadian Journal of Zoology | volume = 77 | issue = 12| pages = 1901–1907 | doi=10.1139/z99-169| bibcode = 1999CaJZ...77.1901C }}</ref>

The environmental variations play a large part in reindeer nutrition, as winter nutrition is crucial to adult and neonatal survival rates.<ref>Wilmer, Pat; Stone, Graham; Johnston, Ian (2009). Environmental Physiology of Animals. Wiley. pp. 645–663. {{ISBN|9781405107242}}.</ref> Lichens are a staple during the winter months as they are a readily available food source, which reduces the reliance on stored body reserves.<ref name="Chan-McLeod AC 1999"/> Lichens are a crucial part of the reindeer diet; however, they are less prevalent in the diet of pregnant reindeer compared to non-pregnant individuals. The amount of lichen in a diet is found more in non-pregnant adult diets than pregnant individuals due to the lack of nutritional value. Although lichens are high in carbohydrates, they are lacking in essential proteins that vascular plants provide. The amount of lichen in a diet decreases in latitude, which results in nutritional stress being higher in areas with low lichen abundance.<ref name="Joly Wasser Booth 2015">{{cite journal |last1=Joly |first1=K. |last2=Wasser |first2=S. K. |last3=Booth |first3=R. |date=10 June 2015 |title=Non-Invasive Assessment of the Interrelationships of Diet, Pregnancy Rate, Group Composition, and Physiological and Nutritional Stress of Barren-Ground Caribou in Late Winter |journal=PLOS ONE |volume=10 |issue=6 |at=e0127586 |issn=1932-6203 |doi=10.1371/journal.pone.0127586 |pmid=26061003 |pmc=4464525 |bibcode=2015PLoSO..1027586J |doi-access=free}}</ref>{{rp|6}}

In a study of seasonal light-dark cycles on sleep patterns of female reindeer, researchers performed non-invasive [[electroencephalography]] (EEG) on reindeer kept in a stable at the [[University of Tromsø|UiT The Arctic University of Norway]]. The EEG recordings showed that: (1) the more time reindeer spend ruminating, the less time they spend in [[non-rapid eye movement sleep]] (NREM sleep); and (2) reindeer's brainwaves during rumination resemble the brainwaves present during NREM sleep. These results suggest that, by reducing the time requirement for NREM sleep, reindeer are able to spend more time feeding during the summer months, when food is abundant.<ref>{{cite news |last=Cell Press |date=22 December 2023 |title=Reindeer sleep while chewing their cud |url=https://www.sciencedaily.com/releases/2023/12/231222145453.htm |work=ScienceDaily |location= |access-date=December 25, 2023}}</ref><ref>{{cite journal |last1=Furrer |first1=Melanie |last2=Meier |first2=Sara A. |last3=Jan |first3=Maxime |display-authors=1 |date=December 22, 2023 |title=Reindeer in the Arctic reduce sleep need during rumination |journal=Current Biology |volume=34 |issue=2 |pages=427–433.e5 |doi=10.1016/j.cub.2023.12.012 |doi-access=free |pmid=38141616 |hdl=10037/33347 |hdl-access=free }}</ref>

=== Reproduction and life cycle ===
{{Further|Rut (mammalian reproduction)#Cervidae}}
Reindeer mate in late September to early November, and the gestation period is about 228–234 days.<ref name="Bergerud2014">{{citation |title=Caribou |first=A.T. |last=Bergerud |url=http://www.thecanadianencyclopedia.ca/en/article/caribou/ |publisher=The Canadian Encyclopedia |date=29 April 2014 |access-date=3 September 2014 |url-status=live |archive-url=https://web.archive.org/web/20141207050757/http://www.thecanadianencyclopedia.ca/en/article/caribou/ |archive-date=7 December 2014 }}</ref> During the mating season, bulls battle for access to cows. Two bulls will lock each other's antlers together and try to push each other away. The most dominant bulls can collect as many as 15–20 cows to mate with. A bull will stop eating during this time and lose much of his body fat reserves.<ref name="animalcorner.co.uk">{{cite web|url=http://www.animalcorner.co.uk/wildlife/caribou.html |title=Caribou at Animal Corner |url-status=dead |archive-url=https://web.archive.org/web/20121029063613/http://www.animalcorner.co.uk/wildlife/caribou.html |archive-date=29 October 2012 }}</ref>

To calve, "females travel to isolated, relatively predator-free areas such as islands in lakes, peatlands, lake-shores, or tundra."<ref name="SARA2014" /> As females select the habitat for the birth of their calves, they are warier than males.<ref name="Bergerud2014" /> Dugmore noted that, in their seasonal migrations, the herd follows a female for that reason.<ref name="Dugmore1913" /> Newborns weigh on average {{cvt|6|kg}}.<ref name="Naughton2011" /> In May or June, the calves are born.<ref name="Bergerud2014" /> After 45 days, the calves are able to graze and forage, but continue suckling until the following autumn when they become independent from their mothers.<ref name="animalcorner.co.uk"/>

Bulls live four years less than the cows, whose maximum longevity is about 17 years. Cows with a normal body size and who have had sufficient summer nutrition can begin breeding anytime between the ages of 1 and 3 years.<ref name="Bergerud2014" /> When a cow has undergone nutritional stress, it is possible for her to not reproduce for the year.<ref>{{Cite journal |title= Reproductive Pauses by Female Caribou |journal= Journal of Mammalogy |date= 18 February 1994 |issn= 0022-2372 |pages= 10–13 |volume= 75 |issue= 1 |doi= 10.2307/1382230 |first= Raymond D. |last= Cameron |jstor= 1382230 }}</ref> Dominant bulls, those with larger body size and antler racks, inseminate more than one cow a season.

=== 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.

{{clear left}}
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>

{{clear left}}