Natural factors

Natural factors include natural variability in numbers, predators, and competition (described below) and also diseases, parasites, and fire, which are described more fully under the climate change section.

Natural Variability

There are natural variations in the numbers of caribou. This variability is thought to run in cycles, and to be influenced by the overgrazing of habitat when populations are at their peak. Traditional knowledge holders in the NWT have put the cycles of barren-ground caribou at between 10 and 60 years. Scientific studies agree that the population cycles seem to run over several decades.

This variability is not a threat to caribou all by itself, but natural variability can produce low numbers in any given herd or location, and then the low numbers may be driven even lower by other threat factors, making it harder for the caribou to rebound. The rate of change of caribou herds can be steep. For instance, the George River and Leaf River herds increase or decrease at rates of up to 15% a year. That means a herd can double in less than ten years - or its numbers can be halved.   


Wolves are the main predators on the caribou populations of the Canadian Arctic. One three-year NWT study found that in three-quarters of wolves sampled, about two-thirds of their stomach contents were from caribou. Grizzly bears are another major predator, and in some cases depend heavily on caribou for their diet. They not only kill caribou, but also scavenge caribou killed by wolves or hunters. Black bears, lynx, wolverines, and even golden eagles are also among animals that will attack and eat full-grown caribou or calves. There are concerns that as other animals (such as moose and deer) move into caribou territory, they can maintain higher populations of caribou predators.


There are different views as to how much caribou compete with other animals for food sources, and whether this competition would affect the numbers of caribou, or their choice of range. According to some Indigenous knowledge sources, the presence of muskoxen in an area can reduce food available to caribou. Some Indigenous people believe that caribou do not even like the smell of muskoxen. Some scientific sources also suggest that muskox densities in some places may be detrimental to caribou because of an overlap in what they eat. There is also the potential for more overlap between northern caribou and white-tailed deer and moose. Climate change has allowed these species to expand their range, and they could be competing for some of the same food, and could also introduce new diseases to caribou.

Related news

The Double-Edged Sword of Genetic Diversity in Caribou

A study of caribou genetics finds that "caribou maintain a high level of genetic diversity". This could be both a good thing and a bad thing. Genetic diversity can help species adapt. But when population numbers are low, genes that might harm a herd's ability to survive can become more common in a population. 
29 February 2024 | trent university

Rapid response needed to contain ‘zombie deer’ disease in B.C.

Chronic wasting disease, a brain disease that affects deer species, has been found for the first time in British Columbia. It has not yet been found in caribou in Canada, but is assumed to be capable of spreading to them.
20 February 2024 | National Observer

Caribou Management in Alaska

An Alaska public radio call-in program on the subject of caribou management, including climate change impacts and harvest levels. The program runs just under an hour. Not Canadian, but discussing similar issues.
10 January 2024 | Alaska Public Media

Taking a Bite Out of Caribou Herds

An article written by a researcher looking into the factors affecting the decline of barren ground caribou, particularly the Bathurst herd. The researcher is a member of the "Kutz lab" team that has been working alongside Indigenous communities in the Northwest Territories to investigate causes of the decline, and monitor caribou health. "In the coming year, we are initiating a new project for Central Canadian barren-ground caribou to see whether Indigenous knowledge of caribou health, coupled with harvester-based sampling and local field observations, can anticipate population shifts for proactive management."
14 December 2023 | fair chase magazine

Where Are All the Caribou?

A magazine length story talking about the general decline of barren-ground caribou and the impacts of that deline on local people. The story includes a focus on the Bathurst Caribou herd, the Western Arctic herd in Alaska, and a mention of the Porcupine herd. The story mentions various possible factors in the decline with making any conclusions.
20 November 2023 | National geographic

Researcher illustrates animal behaviour in wildfire-burned forest

A story about a researcher investigating wildlife use of burned forest in the Northest Territories. Although the research focuses on caribou, the story mentions some evidence that moose are favouring recently burned forest areas. 
6 November 2023 | cbc north

OPINION: Alaska’s game management goals for Mulchatna caribou are unrealistic

This is another perpsepctive on the decision by the Alaska Department of Fish and Game to undertake large-scale predator control on the range of a migratory caibou herd. The department shot 94 brown bears, along with a few black bears and wolves this spring. While this is not a herd that ranges into Canada, it is an interesting discussion of various aspects of caribou management, including the efficacy of predator control, and the setting of appropriate targets for herd size. 
16 August 2023 | Anchorage Daily News

State wildlife officials trying to revive Southwest Alaska caribou killed almost 100 brown bears in less than a month

A story about predator control in Alaska, where many bears were killed in an effort to aid the declining Mulchatna caribou herd. The top two causes for the decline are reported to be climate change and brucellosis, but state officials say that predator control is the only practical lever they have to try to revive the herd.
12 June 2023 | Anchorage Daily News

University of Saskatchewan researchers intensify efforts to track disease in caribou

A story about a new project to track the extent to which deer populations with chronic wasting disease overlap caribou habitat in northern Saskatchewan. The disease has yet to be found in caribou, but there are concerns that it could spread between different species in the deer family.
11 April 2023 | CBC


The article by two prominent Canadian caribou biologists raises the issue of caribou migration memories. They suggest that caribou migrations are learned behaviour, and that in some herds where numbers have dropped very low, there may be insuffucient collective memory to sustain traditional migration routes.
16 August 2022 | The Circle (WWF)

Transplanting lichen to grow food for threatened caribou

A news story about a pilot project in British Columbia that is attempting to speed up the recovery of forage in winter range for caribou by transplanting lichen. the range for a local caribou herd has been affected my mountain pine beetle infestations, fires, and other distrubances that have reduced the quantity of lichen available for a local caribou herd. The story says that results from the project are "very positive" and that, "Early signs point to this new approach becoming a tool in caribou winter habitat restoration."
21 July 2022 | Prince george citizen

Can beavers catch chronic wasting disease?

A news release about research at the University of Alberta that suggests chronic wasting disease (a disease that affects deer) might also be spread by beavers. The disease has not been shown to exist in caribou, but is increasing in some deer populations in Canada, and the range of infection in also increasing. 
28 June 2022 | Mirage news

Tłı̨chǫ Gov't says caribou herds need 'balance' between conservation, harvesting, industry

A news article that talks about the need to balance the pressures on Northwest Territories caribou herds. The article notes that the Bluenose East herd seem to be recovering, while the Bathurst herd contniues to decline.  
14 March 2022 | CBC north

Caribou cams give insight into secret lives

A news story describing research conducted on the Fortymile caribou herd that involved fitting caribou with GPS collars that also incorporated video cameras. The cameras captured snapshots of what the caribou were feeding on, and other behaviours.
16 February 2022 | Alaska Native News

Manitoba responding to first case of chronic wasting disease

This news story refers to the a first case of chronic wasting disease being found in Manitoba. The brain disease affects several kinds of deer. The province licenced a special hunt of deer in the area where the infected animal was found, but no further cases were reported. 
11 January 2022 | Ontario out of doors magazine

Study on Yukon Southern Lakes wolves a 'success story,' researcher says

A wolf study in southern Yukon is finding that wolves are not stopping the recovery of local herds. The study found that while wolves are killing caribou, most of their diet is made up of moose. Tow local caribou herds (Carcross and Ibex) have been recovering numbers over the past twenty years.
22 December 2021 | cbc north

NWT ENR asks hunters for moose heads

The government of the Northwest Territories is paying hunters to give them boreal caribou heads, moose heads, or white-tailed deer heads. The government plans to check the heads for signs of chronic wasting disease, a brain disease that has been found in deer species in Saskatchewan and Alberta. No cases have yet been found in caribou, and no cases have been found in the NWT. 
31 August 2021 | Northern News Services

Highly Contagious Bacteria Infects Mulchatna Caribou Herd

This 18'15" interview focuses mostly on the incidence of the disease brucellosis in the Mulchatna caribou herd in Alaska but also touches on other diseases and parasites, and the connection to climate change. The migratory southwest Alaskan herd has suffered declines similar to those seen in much of northern Canada.
23 July 2021 | KYUK (Alaska)

Habitat restoration may be alternative to wolf cull, says study

A news story about research into the effects of seismic lines lines and roads on wolves' access to caribou. The study obstructed some lines and roads with natural barriers, making them more like the surrounding bush. According to the story, encounters between wolves and caribou dropped dramatically where the access routes has been obstructed. The story also quotes a professor of ecology saying "...this study is just the first baby step in looking at whether an alternate approach like this could have the same results as what you see with wolf control."
17 June 2021 | Cabin Radio (NWT)

The delicate art of stabilizing Yukon’s Fortymile caribou herd

A feature-length article on the new management plan for the Fortymile caribou herd in Yukon. The article talks about the role of hunting in managing the herd size, and the comanagement plans for the herd split between the Yukon government and the Tr’ondëk Hwëch’in First Nation.
21 December 2020 | The Narwhal

N.W.T. wolf cull 'inhumane and unnecessary,' says Łutsel K'e Dene First Nation

This news story quotes a submission by the Łutsel K'e Dene First Nation to an official request by the NWT and Tlicho governments for feedback on plans to cull wolves. The wolf-culling program is intended to help protect the Bluenose East and Bathurst caribou herds. Both of them have declined dramatically in the past few years. The First Nation's letter calls the wolf-culling plan "inhumane and unnecessary".
17 November 2020 | CBC North

N.W.T. harvesters will get more training to kill wolves, help caribou population

A story about the NWT and Tłı̨chǫ governments' plans to help train local harvesters to kills wolves. This is part of the attempt to reduce wolf predation on the Bathurst and Bluenose East caribou herds. At the moment only one person in theTłı̨chǫ comunities targets wolves.
28 August 2020 | CBC

Researchers watching the balance between Nunavik’s wolves and caribou

The Quebec government is responding to reports of increasing wolf predation on the Leaf River herd by satellite collaring wolves to track their level of caribou predation. The story also mentions that the provincial government is working on a management plan for the Leaf River herd.
26 May 2020 | Nunatsiaq News

Tlicho, N.W.T. govt's submit joint wolf management plan to support caribou recovery

A 2020 news story on a proposed new wolf management plan affecting the Bluenose-East and Bathurst herds.
3 February 2020 | CBC

Where are the wolves? Satellite collaring planned for wolves on caribou winter range

a 2020 news story about collaring wolves associated with the Beverly/Ahiak, Bathurst and Bluenose-east herds.
31 January 2020 | CBC

Communities 'supporting each other' to conserve Bluenose East herd

A 2019 news story that includes suggestions that wolves are to blame for summer range losses for two NWT caribou herds. The story also talks about Indigenous management.
11 April 2019 | CBC

Killing wolves won't save caribou herds, experts say

A 2019 news story quoting two biologists who argue that wolf predation is not the major problem in driving the current caribou declines
27 February 2019 | CBC

Is Warming Bringing a Wave of New Diseases to Arctic Wildlife?

Rapid warming and vanishing sea ice in the Arctic has enabled new species, from humpback whales to white-tailed deer, to spread northward. Scientists are increasingly concerned that some of these new arrivals may be bringing dangerous pathogens that could disrupt the region’s fragile ecosystems.
6 November 2018 | Yale 360

Starvation after weather event killed caribou on remote Arctic island

Icy crust on snow may have prevented caribou from digging for lichen
2 February 2017 | CBC

Related resources

Effectiveness of population-based recovery actions for threatened southern mountain caribou

This is an academic analysis of the factors affecting southern mountain caribou decline and recovery. It offers some hope, showing that some management efforts such as predator (wolf) control are helping with the recovery of some herds, but warns that the long term solution must include habitat protection and restoration. While the herds studied are smaller and more geographically limited than migratory caribou, there may be some applicability to management of northern herds.

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Managing predatorsClimate changeHuman disturbanceNatural factors

Shifting trails: the shrinking range of Bathurst Caribou

An excellent new web-based resource including maps and multimedia that gives a clear description of the challenges faced by the endangered Bathurst caribou herd, and the impacts of the herd's decline on the Tłı̨chǫ. The Tłı̨chǫ are a first nation whose territories to the north of Great Slave Lake overlap with the wintering range of the Bathurst herd. This site is a good case study of the challenges facing this herd and other barren ground caribou herds.
"Fate of the Caribou" project and partners (2023)

Evidence of migratory coupling between grey wolves and migratory caribou

An academic paper examining movement of wolves following caribou herds in Northern Quebec.

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Barren-groundLeaf RiverManaging predatorsNatural factors

Government of Canada invests $3.8 million to support barrenground caribou conservation in the Northwest Territories

A news release from the Canadian government department of Environment and Climate Change announcing an investment in three caribou projects of $3.8 million, to be matched equally by the government of the Northwest Territories. the releqase says the projects, "will monitor barren-ground caribou, their habitats, and threats that may be affecting herds in the Northwest Territories by using Indigenous and Western science and knowledge. Projects also aim to conserve and protect barren-ground caribou populations and their habitats by working to minimize human and predator impacts, and identifying important barren-ground caribou habitats such as calving grounds and migratory routes for conservation." The release doesn't mention the exact nature of the projects, or the period over which the money will be paid out.
Environment and Climate Change Canada (2022)

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Barren-groundRange managementClimate changeHuman disturbanceNatural factors

Behaviour is more important than thermal performance for an Arctic host–parasite system under climate change

An academic paper reporting on combined experimentation and modeling to try to assess the effects of climate change on a common caribou/reindeer gut parasite. The paper found that not just changing temperatures, but the ways in which parasites may change their behaviours, and ways in which caribou may also change theoir behaviours are likely to be more important factors.

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Wolf culls change hunting habits and help caribou conservation

An article based on research into wolf habits in northeast Alberta after culling prompted by caribou conservation. The article found that remaining wolves in an area where wolves have been culled shift to a more nocturnal hunting pattern. The article suggests that "If wolves are not active at the same time as large ungulates, predation rates decrease. This will likely contribute to recovering caribou population growth." 

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Managing predatorsNatural factors

Caribou gut parasites indirectly create a greener tundra

An article about research into the ecological impact of gut parasites in caribou. The researchers "...developed a series of mathematical simulations to test how caribou survival, reproduction and feeding rate could be influenced by stomach worm (Ostertagia spp.) infections." They found that the effects of infection are similar to predation, with more plant growth being the end result of caribou sickened or killed by parasites. The authors suggest that changes in the abundance of parasites should be a factor considered in ecosystemic change.

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Natural factors

Update on the global status of wild reindeer and caribou

This online article gives a relatively brief overview of the status of wild caribou and reindeer around the circumpolar world. There are some bright spots, but, "At the global scale, the historical trend continues with declining abundance and contracting distribution for most Rangifer populations." The global population of wild caribou and reindeer is estimated ar 2.43 million, down from 2.8 million in 2016.

The importance of ranges and habitat for the Porcupine Caribou Herd

A good simple and visually interesting web page/infographic that explains the importance of the different parts of the Porcupine caribou herd range. Ideal for younger audiences as a learning tool. Although specific to the Porcupine herd, it could also be used to explain the importance of range for other migratory caribou herds.

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PorcupineBarren-groundRange managementNatural factors

Reasons for Decisions Related to a Joint Proposal for Dìga (Wolf) Management in Wek’èezhìı

A 109-page document on the reasons for decision of the Wek’èezhìı Renewable Resources Board regarding wolf management in the region. The co-management board makes recommendations to the Tlicho and Northwest Territories governments, covering an area north and west of Yellowknife. The report supports continuing to kill wolves as a way of helping the recovery of the Bathurst and Bluenose East caribou herds. 
Wek’èezhìı Renewable Resources Board (2021)

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BathurstBluenose EastManaging predatorsNatural factors

Caribou and reindeer migrations in the changing Arctic

This academic paper looks at factors that affect caribou migration, including climate change and development. it concludes, "...we recommend that large areas of undeveloped critical habitat, like calving grounds, be protected to conserve Rangifer. Where barriers exist, or will exist, migrations will be altered or lost."
Animal Migration (2021)

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This 12-page document gives brief summaries about work on muskox and caribou in the central Arctic region of Canada (communities of Ulukhaktok, Kugluktuk and Cambridge Bay). The research centres on the health of the two species, and includes projects to gather Indigenous knowledge on the Dolphin and Union herd, and disease prevalence in the Bluenose East herd. The research is not yet complete so few conclusions are drawn.

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Barren-groundBluenose EastDolphin and UnionNatural factors

Video of polar bear hunting an adult caribou

This 2:09 video shows a polar bear swimming up behind an adult male caribou, seizing it, and then dragging it up onto shore.
field and stream (2021)

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Format: video

Natural factors

Large‐scale prion protein genotyping in Canadian caribou populations and potential impact on chronic wasting disease susceptibility

This academic paper is about chronic wasting disease, a brain disease that affects members of the deer family. It has not been found in Canadian caribou yet, but has been found in deer. The genetic makeup of different caribou subspecies is thought to influence their vulnerability to chronic wasting disease. This paper suggests that barren-ground caribou may be less vulnerable than the woodland and mountain caribou.

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Barren-groundRange managementNatural factors

Aerial Survey of Muskoxen (Ovibos moschatus) and Peary Caribou (Rangifer tarandus pearyi) on Northwest Victoria Island, April-May 2015

A 2019 report on a 2016 sruvey of Peary Caribou and muskoxen on northwest Victoria Island. Thousands of muskoxen were seen, but only two caribou.
Government of the Northwest Territories (2019)

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PearyNatural factors

Wolves Hunt Caribou In Quebec’s Northern Forest

An almost 5 minute video clip showing wolves hunting caribou, focuses on the wolves’ hunting techniques. 
CBC (2018)

Format: video

Natural factors

Demography of an increasing caribou herd with restricted wolf control: Caribou Demography and Wolves

A 2017 academic paper on the Fortymile herd focusing on wolf predation and the impact of overgrazing on herd size. The paper counters earlier opinions that wolf control (lethal and non-lethal) had a significant impact on the herd’s growth. Paper available on request.

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FortymileManaging predatorsNatural factors

Wolf Technical Feasibility Assessment: Options for Managing Wolves on the Range of the Bathurst Barren-ground Caribou Herd

A 2017 assessment of options for wolf control on the range of the Bathurst caribou herd. Assessment criteria include humaneness, efficiency, effectiveness, and risks.
Wekʼèezhìi Renewable Resources Board (WRRB) (2017)

Technical Report on Cape Bathurst, Bluenose-West and Bluenose-East Caribou Herds

A 90-page 2016 report presenting scientific knowledge and status of the Cape Bathurst, BluenoseWest and Bluenose-East caribou herds and gaps in knowledge.  One of two companion documents to "Taking Care of Caribou: The Cape Bathurst, Bluenose-West and Bluenose-East Caribou Herds Management Plan"
Government of the Northwest Territories (2016)

Peary Caribou and Muskox Survey of the Melville-Prince Patrick Complex, Northwest Territories and Nunavut Summer 2012

A 21-page 2016 report on a 2012 aerial survey of Peary caribou and muskoxen on several Arctic islands shared by the NWT and Nunavut.
Government of the Northwest Territories (2016)

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PearyWestern Queen ElizabethNatural factors

Aerial Survey of Peary Caribou and Muskoxen on Banks Island, July 2014

A 24-page report of an aerial survey of Peary caribou and muskoxen on Banks Island in the Inuvialuit Settlement Region of the Northwest Territories.
Government of the Northwest Territories (2014)

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PearyBanks-VictoriaNatural factors

Engaging Bluenose Caribou Communities

This lengthy 2014 report contain notes from all the community meetings that fed into the management plan for three herds (Bluenose-East and West and Cape Bathurst). It is the result of consultation sessions in 17 communities in the NWT and Nunavut. It contains much Indigneous knowledge about the caribou, but the report cautions that it “...should not be seen as a complete record of the traditional and community knowledge that exists about these caribou.”
Wekʼèezhìi Renewable Resources Board (WRRB) (2014)

Weather-based Indices of Parasitic Fly Activity and Abundance for the Bathurst Caribou Post-calving and Summer Range: Users Guide

A specialized 2014 report on the linkages between climate and levels of insects that bother caribou on the post-caling/summer range of the Bathurst Caribou herd.
Government of the Northwest Territories (2014)

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BathurstNatural factors

Working together for Baffin Island Caribou

A brief 2013 workshop report which examines the causes and impacts of the decline of caribou on Baffin Island, and suggests some management measures.
Government of Nunavut (2013)

Population Ecology of Caribou Populations without Predators: Southampton and Coats Island Herds

This paper is a review of the ecology of two caribou populations inhabiting predator-free northern islands, Coats and Southampton Island.

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Format: pdf

Coats IslandSouthampton IslandNatural factors

Enhanced North Slave Wolf Harvest Incentive Program

The enhanced North Slave wolf harvest program run by the Government of the Northwest Territories in the range of the Bathurst and Bluenose-East caribou herds.
Government of the Northwest Territories