How Do Wildlife Survive the Winter?

How Do Wildlife Survive the Winter?

Central Oregon winters can be tough. With freezing temperatures and snow falling, we’re not the only ones thinking of what we can do to stay warm. Unlike humans, wildlife don’t have heaters or extra layers readily available as soon as they get cold. While we like to cozy up at home with a blanket and a warm drink, Central Oregon wildlife have unique behavioral and biological adaptations in order to survive the cold, snowy months. 

While there are some extraordinary methods used by wildlife to survive tough winters, most wildlife will either go through some type of hibernation, migrate to warmer places, or bulk up and tough it out during winter months. 

Some species of frogs can make their own antifreeze to protect their vital organs during cold weather. You can learn more about this method and other methods reptiles and amphibians use in the winter on our blog post How do Central Oregon Reptiles and Amphibians Stay Alive in the Winter?. However, most Central Oregon wildlife don’t have the luxury of creating a freeze proof concoction in their bodies when temperatures drop. 

Do you ever wonder how the tiny Anna’s Hummingbird is able to survive the harsh Central Oregon winters or how our local rodents last several months without any fresh greens to eat? The answer is that their bodies undergo short- or long-term physiological changes to help them persist through periods of unfavorable conditions like cold weather and minimal food availability. These strategies of survival are referred to as torpor and hibernation, respectively.

It is a common misconception that hibernation is an extended period of sleep. In actuality, hibernation can range from periods of very minimal activity, including a slowed heartbeat, pace of breathing, and decreased internal body temperatures, to intermittent bouts of activity and “awakeness”. For example, black bears will gorge themselves during the late summer and fall in order to store up their fat reserves. Once they’re nice and fat, they will go into a type of hibernation where they slow down their metabolic rate and wait out the winter in a den. They will wake up and have minimal activity during this dormancy, but rely largely on this “slow period” to survive the winter. Interestingly, hibernation is not just a strategy for overcoming cold winter temperatures. In other parts of the world, tropical mammalian species undergo hibernation to survive the dry seasons that produce less food.

Other Central Oregon wildlife also will go into a dormant state as the weather starts to change known as torpor. Torpor is a similar but often shorter-term phenomenon than hibernation. Like hibernation, torpid individuals experience a decreased metabolic rate and lowered body temperature. Animals in torpor also temporarily stop eating and defecating (McGuire et al. 2010). When torpor lasts for more than 24 hours, the condition of inactivity is considered hibernation (Wilsterman et al. 2019). Torpor is common in nightjars like poorwills and nighthawks. Hummingbirds will also enter a state of torpor where they slow down their metabolism and respiration rate for shorter periods of time to help conserve energy. Read more about the adaptations hummingbirds have to survive the winter on our blog post What Happens to Hummingbirds in the Winter?.

Many reptile and amphibian species will also go into a type of dormancy called brumation. They will burrow in piles of logs or leaf litter or sometimes partially bury themselves in the mud while they slow down their metabolism, heart rate and respiration. Unlike with hibernation, these animals will emerge from their dormant state on warmer winter days. Many insects also hibernate as adults. 

Some wildlife don’t undergo hibernation, torpor, or brumation to survive the winter, but instead leave their breeding grounds altogether when conditions deteriorate. This strategy is called migration, and can range from extremely long-distance journeys to shorter, irruptive movements across the landscape. Wildlife can migrate from north to south and even along elevational gradients depending on resource availability. Wildlife such as Osprey and Swainson’s Hawks are examples of migratory species in Central Oregon. Many other bird species and even some butterfly species will also head south in search of warmer weather. Some travel as far as South America to avoid getting caught up in a snowstorm.

While many species avoid winters by migrating or hunkering down until warmer weather comes, there are several Central Oregon species that remain active during the winter. Unfortunately, some of these animals running on fat reserves don’t survive when food becomes scarce. However, these carcasses act as an important food source for many other Central Oregon wildlife. Some birds of prey and other predators like mountain lions and bobcats will slightly alter their diets in the winter to conserve energy. Many of these predator species will opt for a carrion diet rather than hunting and killing themselves so they can save energy. Many herbivores will bulk up in the summer and fall so that they have enough fat reserves to keep them alive when winter comes and food becomes scarce. 

While many wildlife species store extra food in their bodies, squirrels and other rodents will store up food and “cache” it so they have enough to survive through the winter. Pikas also cache plants in their “haypiles” so they can stay hidden in their dens all winter without having to leave to find food. While food caching seems like a trait only for rodents, there are some wildcats that will bury small prey to save as a last resort meal in the winter. Higher elevation birds such as gray jays are also known for caching food in the grooves of tree bark. However, climate change impacts the ability of these species to exhibit this behavior since cached food can go bad in unseasonably warm winter weather. 

Another adaptation many year round residents use to stay warm during the freezing months includes growing a thick winter coat. Many mammals such as the Sierra Nevada red fox, elk, and beaver grow a dense, thick layer of fur to help insulate their bodies during the winter. Beavers also secrete oils with which to coat their fur to help keep them dry and warm.

Between migrating, hibernating, storing up food, and growing a warm, furry coat, Central Oregon wildlife are well equipped for winter. If you want to help out wildlife during this harsh season, the best thing you can do for them is give them space. Wildlife can easily become stressed out and waste energy trying to avoid human activity and disturbances. If you come across an animal that appears especially lethargic, unresponsive or even dead, consider if the individual might be torpid! Hummingbirds, for example, can look injured or deceased while in torpor because they often hang upside down from a bird feeder or branch while in this state. If you are worried an animal is sick or injured, call our wildlife hotline at (541) 241-8680.

Works Cited:

McGuire, N. L., et al. “Seasonality: hormones and behavior.” Encyclopedia of animal behavior 3 (2010): 108-118.

Wilsterman, Kathryn, et al. “20688 Seasonality: Hormones and Behavior.” (2017).
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