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

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

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)

Usage: Non-commercial with attribution
Format: web

BathurstBluenose EastManaging predatorsNatural 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.

Usage: Non-commercial with attribution
Format: web

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)

Usage: Non-commercial with attribution
Format: pdf

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

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)

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.

Usage: On request
Format: web

FortymileManaging predatorsNatural factors

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)

Usage: Non-commercial with attribution
Format: pdf

PearyWestern Queen ElizabethNatural factors

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)

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)

Usage: Non-commercial with attribution
Format: pdf

PearyBanks-VictoriaNatural factors

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)

Usage: Non-commercial with attribution
Format: pdf

BathurstNatural 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)

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.

Usage: On request
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