by Elise Gundlach, certified wildlife rehabilitator and WildCare operations director, and Kristy Wicker, WildCare education director
Photos courtesy of WildCare Oklahoma
Have you ever wondered what wild animals in Oklahoma do during the winter? Wildlife have developed unique adaptations and different strategies for surviving colder temperatures and shorter days. Some animals such as deer, squirrels, beavers, and songbirds remain active throughout the winter. Others such as scissor-tailed flycatchers, sharp-shinned hawks, and Mexican free-tailed bats migrate south to warmer areas. But how do animals survive cold temperatures and limited food sources during the winter? Where do all the turtles go?
What Makes Reptiles and Amphibians Different?
Reptiles and amphibians are ectotherms — their body temperatures change to match the temperature of their surroundings. Turtles, frogs, snakes, and lizards do not have thick fur coats or downy feathers to provide insulation. However, they do have special physiological adaptations and behavioral strategies to help them survive winter weather.
Many reptiles go through brumation, similar to hibernation, during which a mammal goes into a low-energy state. Brumation is a period of dormancy when turtles, snakes, frogs, and salamanders reduce their activity levels, metabolism, and heart rates to survive the stressful environmental conditions of winter.
During brumation, animals can survive for months without food and with little oxygen. Interestingly, reptiles and amphibians can use brumation to survive intense heat and drought events too. That might become more relevant as heat waves and droughts increase in frequency and intensity.
How Does Brumation Work?
In the fall, turtles, for example, will start to eat less each day. They become more sluggish as temperatures decrease and hours of daylight lessen. Many land-dwelling reptiles will burrow into the ground and bury themselves in soil, mud, burrows, or leaf piles or under logs and rocks. Aquatic reptiles — those that live primarily in water — will often rest on the bottom of ponds or creeks to wait out the winter as surfaces freeze over.
Although reptiles can’t eat and breathe while underground or underwater, their nutritional and oxygen needs are lower during brumation. They go into an inactive state, shutting down unnecessary body systems or modifying them while living off their fat stores. They can respirate by absorbing oxygen from soil, mud, and water through their skin even when the surface of the water is frozen.
If the surface of the pond remains frozen for too long, oxygen in the mud and water can become depleted. Some turtles such as snapping turtles can shift to anaerobic respiration, which metabolizes stored energy without oxygen. However, this creates lactic-acid toxins in the body, which are neutralized by dissolving calcium and carbonate from the animals’ shells and skeletons — much like an antacid.
Instead of breathing, the animals can use cloacal respiration to supply their bodies with oxygen. They have special blood vessels in their cloacal chamber to absorb oxygen for respiration. In that state, they wait out the winter until the warmer spring months when they become more active. Then they emerge from the ground or to the surface of the water.
Amphibians such as frogs and toads also have a wide variety of ways they survive winter through brumation. Like reptiles, amphibians slow their metabolism and eat less, especially as insect populations decline. Some toads burrow into mud and wet substrates, and others burrow into heavy leaf litter. Other amphibians stay in the water.
Some frogs freeze solid during winter. Those amphibians have developed a unique adaptation — their livers produce substantial amounts of glucose to increase blood-sugar levels, which acts as a natural antifreeze. This limits the formation of ice crystals in the body, including vital organs. This physiological adaptation is called cryoprotection. In springtime, the amphibians will “thaw out” in just a few hours — the heart and lungs amazingly start to work again. But if temperatures warm and then suddenly freeze again, the effects can be deadly — already awakened toads and frogs can die from what is called winterkill.
Interestingly, fish do not brumate but enter a semidormant state called torpor during winter.
Do Mammals and Birds Hibernate?
In winter, some mammals go through a true hibernation, and others might go into torpor state. In true hibernation, a mammal decreases its body temperature and slows its metabolism and breathing rate. Hibernating animals enter that state because of their internal biological clocks, not because of changes in temperature or daylight.
Torpor is an involuntary response to extreme resource-constrained conditions. Body temperatures drop and activity is limited or eliminated in a torpor state, but it might not be for a prolonged period of time. Torpor can last hours, a few days, or weeks. Most animals go in and out of torpor as conditions dictate throughout the winter. Bats often go into torpor when temperatures drop even before true winter sets in.
Although many birds migrate, some also use torpor to survive extreme conditions — doves, pigeons, and some hummingbirds. However, the common poorwill, a member of the nightjar family, is unique in its ability to enter torpor for prolonged periods of time.
Helping Animals through the Winter
Any animal, whether brumating, hibernating, or entering torpor states, must have plenty of fat stores for winter.
Animals survive only if they are healthy before going into extreme-condition survival states. That means ensuring that they have plenty of insects, prey, and vegetation in the months leading up to winter. The key thing people can do is to stop using insecticides, rodenticides, and herbicides that eliminate and poison the animals’ food sources.
In addition, remember to “leave the leaves.” Leaf litter provides winter habitat for reptiles, amphibians, mammals, insects, and birds such as the common poorwill. As leaves decompose, they enrich the soil, contributing to the health of trees, plants, and grass.
Finally, if we have a cold snap after a warming trend during the winter, be on the lookout for animals that might need help. Get them to WildCare or another licensed wildlife rehabilitator for care.
