Food sources such as green plants and insects are very scarce during the winter. The biggest challenge faced by hibernating animals is not to survive the cold weather, but rather to find enough food to last through the winter. Hibernation is a state of dormancy (like a deep sleep) that allows the animal to conserve energy and survive the winter with little or no food.
Hibernators prepare for the winter in different ways. Animals like chipmunks and squirrels gather and store food before the winter, while some animals such as groundhogs and bears eat extra food in the fall to store energy as body fat.
True hibernators go into a very deep sleep where their metabolism is suppressed, their body temperature drops and their breathing and heart rate slow down significantly. They are very difficult to wake up and may even appear dead. This is very dangerous if a predator attacks, so true hibernators find a safe den – a hibernaculum – to survive the winter. True hibernators include the jumping mouse, little brown bat, eastern chipmunk, and woodchuck.
Other hibernators, such as skunks, raccoons, and bears, don’t experience such a dramatic change in temperature, heart rate, or breathing. Instead, they can enter a torpor where their metabolism slows, but they can be woken up more easily. They can sleep during the coldest periods but wake up to escape predators, or to roam and eat during milder weather.
Which species hibernate in Ontario?
Many species found in Ontario hibernate during the winter, including mammals, reptiles, amphibians, and even insects. Let take a look at some of these species:
- Black bears can hibernate for two to seven months depending on latitude and weather. They make their dens in hollow trees or spaces under the roots. They can build up to a five-inch layer of body fat in the fall, which sustains them through the winter.
- Bats congregate in caves in the thousands to hibernate. The resting heart rate of an active bat is usually between 300 and 400 beats per minute, compared to 10 beats per minute for a hibernating bat!
- Ontario snakes, from the common garter snake to the Massassauga rattlesnake, hibernate from as early as October in groups that can include their own species as well as other species of snakes. They occasionally come out their burrows to bask in the sun.
- Turtles such as the Blanding’s turtle hibernate in a range of locations including marshes and swamps.
- Frogs and toads have different hibernation strategies: spring peepers and woodfrogs hibernate under leaf litter, logs or rocks and can prevent freezing by producing more glucose in their organs, which does not freeze. Northern leopard frogs, bullfrogs and green frogs hibernate underwater in water bodies that are deep enough to prevent freezing.
- In the fall, an entire colony of bumblebees dies except for the queen, who hibernates over the winter and builds a new nest to lay her eggs in the spring.
Different animals have different triggers that let them know it’s time to hibernate. For some, temperature determines hibernation, so a long cold winter will result in a longer hibernation period. Other species go by their food supply and go into hibernation when that supply becomes low. If they have enough food to last the winter they might not go into hibernation at all. Day length can be a trigger for some species, and some seem to have a reliable “internal clock” that tells them when to hibernate, although this is not well understood by scientists.
In the spring, animals spend their remaining energy to rewarm themselves, and must find food sources again quickly in order to enjoy another spring and summer.