Dealing With Winter
How do you stay warm in the winter? Animals and plants have developed incredible techniques to survive cold weather. Read on to learn more about frozen frogs, shivering squirrels, and trees' natural antifreeze!
After our first cold snap, I frantically prepared for winter. I stocked up on long underwear, extra sweaters, and thick wool socks. Luckily, it’s pretty easy for us to bundle up and stay warm, but what about other living things? Animals and plants alike have fascinating strategies to help them survive the winter.
In the winter, deciduous trees fall dormant — a plant’s version of hibernation. Essentially, the tree slows its metabolism and growth rate, and only expends energy if necessary. Abscission — the fancy word for losing leaves— helps trees retain water and energy. Evergreen trees generally avoid abscission. Instead, their needles are covered in a waxy coating which prevents water loss.
Cellular freezing is the biggest threat cold weather poses to trees. As a result, most woody plants have developed incredible cellular adaptations to survive. Cell walls become more flexible, allowing water to pass out of the cell and freeze around special molecules called ice nucleators. The high sugar content left inside the cell (think: maple syrup) prevents freezing. Some trees even produce their own antifreeze proteins! This adaptation is generally referred to as supercooling - a process in which a substance remains a viscous liquid far below its freezing point.
Surprisingly, the process trees go through isn’t too different from the hibernation of frogs! Unlike turtles, frogs can’t bury themselves during the winter. Aquatic frogs, like American bullfrogs, find oxygen-rich water to hibernate and float a couple of inches above the bottom until springtime. As temperatures drop, frogs actually freeze! Ice crystals form under their skin, in their body cavity, and bladder. Their heart and lungs slow, and eventually stop. However, frogs have a high concentration of sugar in their essential organs, which prevents them from freezing. When spring rolls around, frogs need a few days to rest while their body heals any damaged cells. An American bullfrog will go through this process its whole life - up to ten years!
A surprisingly cold-resistant critter, the eastern gray squirrel doesn’t need to hibernate. Autumn is the squirrel’s busiest season. They split their time between “caching” (burying food for later) and eating to build up a warm layer of fat. The caching process is surprisingly complex. Gray squirrels scatter their hoards across an area of up to seven acres! Squirrels sort their nuts by type and then bury each type in its own specific place. They also crack nuts before burying them to prevent them from sprouting. The caching behavior of gray squirrels implies that their memory is much better than we thought! Having stocked their pantry, squirrels turn their focus to staying warm. In the winter, squirrels share their dens with each other to keep cozy. They also are champion shiverers. Yes, one of the most effective ways squirrels stay warm is shivering!
Haverford’s foxes are still out and about, too. Red foxes are extremely adaptable to changing weather conditions and food sources. Their coats are made up of three different types of fur: underfur or awn hairs to provide insulation, wiry guard hairs which help with water resistance, and intermediate hairs which contribute to both. Unlike domestic dogs, foxes grow fur on the bottom of their paws to keep them warm and silence their footsteps. During the winter, foxes’ dens are usually reserved for their kits. Adult foxes have no problem curling up under fluffy tails in the snow! In summer, their diets largely consist of vegetables and berries, but as those plants fall dormant, foxes switch to eating small rodents throughout the winter.
These incredible adaptations are the result of centuries of evolution, and allow animals and plants today to survive winter without batting an eye. If you’re walking past the Haverfarm or in the Pinetum, keep an eye out for these adorable friends!