How Do Wildlife Survive the Winter?
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”. 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.
Torpor, on the other hand, 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 hummingbirds and nightjars like poorwills and nighthawks.
Some wildlife don’t undergo hibernation or torpor 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.
Though our Central Oregon wildlife possess unique adaptations that allow them to survive our long winters, there are a few ways that you can support wildlife over the course of the colder months. One way to help overwintering hummingbirds is to offer a heated food source that won’t freeze in extreme temperatures. Though heated feeders are a great way to offer nectar year-round, it is always important to make sure that they are being cleaned regularly to prevent disease transmission and that you continue to offer the food source for the duration of the winter.
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 ever unsure if an animal might need assistance, we encourage you to reach out to your local wildlife professional for guidance.
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).