Wildlife Survival in Extreme Heat Events

by Jul 16, 2021Conservation


Western Canada, like many parts of western North America has been experiencing extreme hot temperatures early in the summer of 2021. New record-breaking hot temperatures are being documented on daily basis in many parts of the country. While staying cool at home is a priority for me, my concerns during this extreme heat naturally gravitate to the welfare of the wildlife that I care so deeply about.

Scientists have warned that if the planet continues heating at the current rate the changes in habitat driven by climate change could cause half of all wildlife to lose more than 50 percent of their habitat by the year 2100.  One study I read stated that climate change is not just about a steady increase in temperatures it is also about sudden extreme temperature events that can put wildlife into shock and jeopardize their survival.

A growing number of research studies are showing that warming temperatures are increasing the mortality of terrestrial and marine wildlife in all regions of the planet.  Researchers warn that heat stress caused by extreme heat events could become a significant cause of future wildlife extinctions.

The intense heat waves that swept across Australia in recent years caused mass death of tens of thousands wildlife including threatened species. Some research suggest that wildlife species can and have evolved and adapted to gradual changes in climate, but many species will never be able to evolve to hotter climates when individual mortality is high during sudden extreme “shock” heat events. One study reported that wildlife species that rely on microclimate habitats to escape hot temperatures are the species that have declined the most.

Many wildlife species around the world are not just dealing with climate change and extreme heat events they are struggling to cope and adapt to multiple cumulative impacts of which climate change is just one factor. It is becoming more evident in the scientific literature that the effects of heat stress on wildlife that are experiencing temperatures that are hotter than what they are adapted to is taking its toll on many species.

To learn more about what wildlife experts in Canada had to say about the impacts that extreme heat events might have on a few key wildlife species in Canada, I reached out to several experts and asked them these two questions:

  1. How might individual animals cope and adapt to extreme heat events?
  2. What sort of long-term impacts might you expect to wildlife populations or to the species if these types of extreme heat events continue in the years to come?

Here’s what they had to say,


Bighorn Sheep and Mountain Goats

Dr. Marco Festa-Bianchet


University of Sherbrooke, Department of Biology

When we consider weather effects on bighorn sheep and mountain goats in Canada, we tend to think of rain as generally good and deep, crusty snow as generally bad. Temperature rarely plays a large role, except that hot summers are associated with less rain and rapid loss of nutrients in forage. Warmer springs/summers are associated with greater horn growth in bighorn sheep and Alpine ibex, lower growth in Alpine chamois. We have never seen heat like this past summer – if temperatures remain at more than 40˚C for days and there is little cooling at night, we may see mortality directly caused by heat. Heat-cause deaths have been reported for flying foxes, koalas and kangaroos in Australia, mammals adapted to hot arid weather. We teach in statistics not to extend regression lines past the known range of measurements. We are now entering the unknown.


Melanie Dickie, PhD Candidate


Research Coordinator, University of Alberta | ABMI | Caribou Monitoring Unit

There isn’t a ton of research out there on these shorter-term extreme weather events. It’s definitely becoming more worrisome as extreme weather events become more common. A total guess here: I’d expect they would decrease activity and perhaps shift to activity during cooler parts of the day. I’d imagine boreal caribou might spend more time in wetlands, and mountain caribou in any leftover snow patches or in wet shady spots.

Longer-term, increased extreme heat events and warmer, drier weather likely means increased insect harassment and decreased resource quality (decreased nitrogen content). Extreme heat events also means that forest fires are likely to continue to increase, and this is true for within caribou habitat as well. While we don’t have much evidence that fires impact caribou survival per se, caribou do avoid burns. Burns in some forest types can result in increased forage for species like moose and deer; which bolsters predator densities and is bad news for caribou.

Deer and Elk

Dr. Adam T. Ford

Associate Professor, Canada Research Chair in Wildlife Restoration Ecology

Department of Biology, University of British Columbia,

The science isn’t rich on this subject for large mammals. We are dealing with relatively unprecedented temperatures, so our normal tools of the trade – trail cameras, GPS, demography – are not going to reveal these insights until we get a few more of these ‘heat dome’ events while established studies are underway (long term monitoring is key!). And by all credible accounts, there are more heat domes coming.

For the direct effects of heat, my guess is deer will do ‘fine’. So long as there is suitable habitat – access to water, shade, high elevation summer range. A large animal like a deer can probably alter its activities enough to make it through a week or so of intense heat. Will it be comfortable or optimal? No. But it won’t be a massive die off like we see with marine intertidal life.

The indirect effects may be more impactful and complicated. Extreme heat is going to cure off summer forage sooner, likely decreasing the nutritional landscape. It may also make fires more likely, and if in the right place and time, fire provides deer with better forage conditions. If water (see: drought/logging), shade (canopy cover-> logging), or migratory routes are cutoff by roads, fences, or disturbance, then the behavioural and physiological coping mechanisms deer have wont work and animals may suffer heat related stress. This stress could reduce fitness survival and recruitment.

Because cities occur at low elevation where it is hotter, and people tend to protect their irrigated plants from deer, it’s likely that urban deer will suffer more than deer living in more wild places. Hard to say for sure, as there are so many resource ‘subsidies’ in the urban environment. We may learn more about ‘hot’ urban deer after this summer.

More chronic changes in temperature are a different story. Rather than just a pulse of heat, climatic shifts will alter food webs in BC. This will make it easier for new competitors to get a foothold, like white tailed deer. It may also push good quality forage outside of winter range where silvicultural prescriptions are intended to provide food in the winter. These changes mean that we need to keep an eye on climate when planning winter range forestry deferrals and other protected areas.

Polar Bears

Dr. Andrew Derocher

Professor, Faculty of Science – Biological Sciences

University of Alberta

Polar bears evolved to exploit the ecological niche that includes frozen oceans, extreme cold, and top predator of ice-associated seals. The ancestral root of polar bears, brown (grizzly) bears, are well-suited to extreme heat (e.g., living in the Gobi Desert, historically in Mexico and California), but many adaptations of polar bears evolved to minimize heat loss. The small ears, thick fat layer, furred paws, water-repelling fur, and large body size are all designed to keep polar bears warm. In extreme heat, such adaptation become a liability. Polar bears in parts of their range are exposed to a huge temperature across the year: -40°C to +30°C wouldn’t be uncommon but at the upper end, the bears have to adjust their behaviour to keep cool. Some bears will head for the ocean or a lake in summer to keep cool.  The biggest bears monopolize beach ridges with cooling breezes (these also reduce biting insects somewhat). Pregnant females in Hudson Bay may dig dens down to the permafrost that creates a safe, bug-free, microcosm for the summer. The main adaptation is lethargy – when it’s hot, polar bears don’t want to do much of anything. The bears can slow their physiology down a bit and this likely helps conserve some energy.

The biggest impact is loss of sea ice.  Earlier melting of sea ice cuts into the hunting season of the bears and can also prolong the ice-free period with ocean warming that delays freeze-up in the autumn.  The bears can only fast for so long and the resources available on land are inadequate to support a viable population of polar bears.  Over time, areas with extreme heat are likely to lose polar bears. The whole Arctic marine ecosystem is adapted to the prolonged persistence of sea ice. Take away the sea ice or change it too much and a new ecosystem will take over.  We’re seeing this already with increases in temperate species in the Arctic. The changes are occurring from algae to invertebrates to fish and marine mammals.  The new Arctic top marine predator, killer whales will do fine with less or no sea ice.

Grizzly and Black Bears

Dr. Clayton Lamb

Postdoctoral Researcher | Liber Ero Fellow
Universities of British Columbia & Montana

Grizzly and black bears are only active for about half of the year, during which time they accumulate large fat reserves for their time in the den. Although fat reserves and dense fur could be problematically warm during the heat of summer, bears have a number of ways to cope. In the heat, bears generally seek cool areas at high elevation and in north and east facing bowls in the mountains. During these warm times they use cooler times of the day and find small seeps of water at elevation to drink and bathe in. Although bears behaviorally adapt and find ways to stay cool during warm spells, they endure very warm temperatures—sometimes 40C—when preferred foods such as huckleberry are available. Interestingly, bears do not appear to be able to feed on huckleberry at night when it is cooler, perhaps because they are less efficient foraging on berries in the dark. Extreme heat likely reduces bears’ ability to forage as they spend less time feeding when it is warm, and more energy staying cool.

While climate change has the potential to increase a variety of bear foods, shifting phenology (when berries and other foods are available) and winter onset has the potential to change bear behavior in ways we do not yet understand. Bears use of the landscape is currently well matched with timing of spring greening, berry ripening, or salmon runs. As the timing of these energy flows change, it remains to be seen how bears will adapt. As winters change, bears will likely need to shift their location and timing of denning in response. Overall, bears are quite adaptable animals, partly due to their broad ominivorous diet, but shifting climates and extreme heatwaves will present novel challenges that could shift bear behavior and possibly increase human-bear conflicts during this period of transition.


Dr. Roy Rea

Senior Laboratory Instructor

University of Northern British Columbia

Moose, like many other species of wildlife cope with heat through a variety of mechanisms, both physiological and behavioral.  Cooling off during extreme heat where body temperature rises above their thermoneutral zone (where metabolic energy costs are nil or low) costs metabolic energy that could be used for growth and reproduction.  Moose that are already compromised due to poor health are challenged more than healthy moose when air temperatures rise.  Along with ridding heat through evaporative cooling (such as open-mouthed panting) and increasing blood flow to body surfaces and extremities, moose will seek open windy areas, move into water, move up in elevation, seek shade and generally try to use behavioral mechanisms to reduce their heat loading and absorption from the environment.  Like many animals in temperate regions, moose are adapted to cold climates and have a winter coat that they will shed and replace with a summer coat as temperatures warm.  Summer heat stress becomes obvious in moose at between 14 and 24 degrees Celsius.  Moose are one of the largest animals in northern forests and have a relatively low surface area to volume ratio compared to other northern inhabitants and therefore are slower to cool.  Moose that are ‘sick’ and ‘running a temperature’ are more susceptible.

Although clearcuts may be windier than mature forests and allow for exposure to cooling winds, open areas with increased sun exposure do nothing to help moose cool down.  Larger clearcuts reduce usable habitat for moose.  In this respect moose, can retreat to closed canopy forests as a way to find shade and lower temperatures. Thermal cover also provides security cover from predators.  Moose will reduce daytime travel and foraging bouts to stay cool, but this impacts habitat and forage selection at the fine scale.  Lake shores, riparian areas and the forest edges of rivers tend to provide forage (both aquatic and riparian), water and exposure to cool breezes that appear to be preferred by moose at times of increase heat.  Higher wind velocities cool more effectively.  Wind also has the added benefit of driving away biting insects from which moose often seek reprieve.

The intensity and duration of heat events combined with fluctuations in vapor pressure interact to impact moose in complex ways.  Moose have been described by some moose researchers as intolerant to heat with summer temperatures defining their southern distributions.  Increased temperatures due to climate change have been suggested as one reason why moose are struggling to survive at the southern extreme of their range in North America, but debate on the subject exists.  Long term exposure to heat that causes moose to burn energy in an effort to stay cool, will take away from energy resources that moose require for growth and reproduction and may have long term impacts that span many seasons and years for an individual moose.  Many researchers suggest that warming climates will increase the prevalence of pathogens and the susceptibility of moose to them with some researchers suggesting that heat stress negatively impacts the immune system.  Much research remains and research using free-ranging moose fitted with biologgers is likely the kind of data that are required to answer questions about how warming climates will impact various aspects of moose physiology and ecology.




Cover photo Copyright (c) mandritoiu  / Adobe Stock

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