How Do They Do It?
Habitat Enhancing Land Management
“The Old Lakota was wise. He knew that a man’s heart, away from nature, becomes hard; he knew that lack of respect for growing, living things soon leads to lack of respect for humans too.” —Luther Standing Bear
Christine Middleton
BRRRR! I’m Worried About My Wild Friends!
This frozen Pine Siskin was one of many we Master Naturalists found on our properties during Winter Storm Uri, February 2021.
We love those amazing creatures who visit us on our property. But have you ever wondered how they survive cold winter weather?
When Winter Storm Uri, better known as Snow-maggedon, hit Central Texas in February of 2021, some like this poor Pine Siskin didn’t make it.
Eastern bluebirds, robins, and yellow-rumped warblers were also hard hit. And perhaps the most impacted were the bats living under our bridges.
Even some of us with our heated houses, warm clothes, and plenty of blankets struggled through Uri. But we survived, and so did most of our beloved birds and other creatures. But how? And even in less severe winter weather, how do our insects, fish, reptiles, amphibians, birds, and mammals cope when a cold front heads our way?
Yellow-rumped Warbler
Cardinal and Chipping Sparrows
What our favorite creatures do to survive very cold weather depends on a number of factors. First, are they warm blooded or cold blooded? Warm-blooded, or endothermic, animals, such as birds and mammals, maintain a constant body temperature. Endothermic simply means “heated from within” their own body. The inability to maintain that constant temperature during severe cold can be deadly. Some, primarily birds, simply migrate to warmer climates. But most endotherms simply tough it out and rely on some amazing adaptations to protect themselves when conditions turn harsh.
The body temperature of cold-blooded, or ectothermic animals, such as insects, fish, reptiles, and amphibians, depends on their environment. So as the air or water temperature dips, so does their body temperature. But they too have some pretty amazing ways of coping. “Cold blooded” is a misleading term from centuries ago, when people believed frogs or fish were—from their blood— just naturally always cold. But ectothermic means “heated from outside” their bodies. Their bodies cool or warm to match the surrounding air or water. If you overheated your aquarium and discovered fifteen guppies floating at the top, it probably wasn’t overfeeding! And our Blanco River turtles are basking on a sunny river rock to warm up their muscles and raise their heart rate—we endotherms lie out on a warm rock just because it feels nice.
Let’s look at some small cold-blooded creatures among us—insects. Some avoid freezing temperatures altogether by migrating—leaving Central Texas for warmer climates to the south. For example, the Monarch butterflies who delighted us this past fall have by now safely reached their winter retreat in Mexico. Red Fire Ants stay around, unfortunately, but burrow many feet underground to escape the cold.
Monarch passing through Hays County on its way to wintering grounds in Mexico—October, 2022
Other insects have evolved some pretty amazing techniques for keeping deadly ice from forming inside their bodies when the temperature plummets. They produce compounds called cryoprotectants that keep their bodies from freezing when the temperature drops below 32 degrees Fahrenheit. In a sense they are doing the same thing you do when you add antifreeze to your car. The larvae of the Woolly Bear moth and the Goldenrod Gall Fly produce a protein-based antifreeze. And since a lot of the internal structure of an insect’s anatomy is their digestive tract, another strategy involves their emptying their bodies of any liquid form of food, thus preventing ice from forming inside them. And then there are some insects—although we do not know of any such species in Central Texas—who can actually tolerate freezing. When it warms back up, they simply thaw out and go on their merry way.
Other insects use the same strategy most of us do—hunkering down in a warm place until the cold spell passes, perhaps in a crack in the bark of a tree or under a pile of leaves. Then when the weather warms back up, they simply become active again. Still others wait out the entire cold season by burrowing under plant debris or into the soil, protecting themselves from our occasional freezing temperatures here in Central Texas with what you might think of as a layer of insulation. Other insects have evolved their lifecycles so that they simply spend the winter as eggs or larvae, usually underground, under a pile of leaves, or in a dead stalk. Still other adult insects survive in a state of dormancy called brumation.
Hibernation is what some warm-blooded animals, famously bears, do to survive long periods of cold. But what some insects do (along with other coldblooded animals, including turtles, frogs and snakes) is called brumation. Brumation is not quite the same as hibernation because the bodies of cold-blooded animals don’t react to temperature fluctuation in the same way we warm-blooded animals do. Cold-blooded animals first find a protected spot. Then they slow their metabolism as well as their heart and respiratory rates. They essentially become inactive to the point of lethargy. But unlike mammals, they do not fall into a deep sleep. Nor do they fatten up before going into brumation. So brumating critters must wake up periodically to look for food and water. That’s why on a sunny winter day you are likely to see that turtle sunning itself on a warm rock to become mobile enough to eat and drink.
Critters who live in water have a special advantage in that water temperatures don’t fluctuate as much as air temperatures. And warm water tends to sink. So fish can simply hang out at lower depths where the water is somewhat warmer. They also enter a resting state in which their heart slows down and their need for food and oxygen decreases. Aquatic turtles and frogs also escape cold temperatures by hanging out underwater. Turtles dig into the mud at the bottom of a pond or stream. Their metabolism slows down so drastically they stop breathing. But they still need some oxygen, which they are able to get through gas exchange through areas of their throat and tail. Yes, they breathe through their butts, so to speak.
Unlike turtles, frogs don’t completely bury themselves. Rather, frogs just hang out near the bottom or partially buried in the mud. Frogs have lungs, but can also take in some oxygen through their skin. So they rely on oxygen rich water when a cold snap makes it necessary for them to spend an extended period underwater. And, like insects, some frogs can produce antifreeze in the form of higher glucose levels in their blood. Like certain insects, some northern frog species can even survive freezing. What about terrestrial amphibians and reptiles? They too find a good place to shelter from the cold. For amphibians like the Gulf Coast Toad, this means finding a nice warm burrow—a hole at the base of a tree or under a rock ledge. Others might find shelter in leaf litter, or under logs.
Gulf Coast Toad burrowed down in between (and under) rocks and tree roots
Snakes and other reptiles usually find a tree cavity or hang out in an underground burrow. Sometimes only one snake will occupy a burrow. But frequently snakes cluster together as a way of preserving body heat. Texas spiny lizards, six-lined racerunners, and other lizards also find safe places underground to brumate.
Texas Spiny Lizard
Like Monarch butterflies, some birds head south. But how do those who stay all winter—our year round residents (cardinals, chickadees, titmice, …) and our winter visitors (cedar waxwings, robins, pine siskins, ...)—survive when temperatures plummet? In the fall, birds molt and grow more and thicker feathers—more insulation for cold days spent foraging for food. But what other physical adaptations enable them to survive when extreme weather hits Hays County? You may notice birds will appear plumper than they normally do. That’s because they fluff their feathers to create a layer of insulating air underneath.
Yellow-rumped Warbler
Like snakes, birds such as bluebirds huddle together. But that wasn’t enough during Uri, which explains why so many bluebirds didn’t make it through the storm. Hummingbirds have another survival trick when temperatures drop precipitously; they go into a state called torpor.
Torpor is somewhat like hibernation, except that it only lasts a short time, perhaps only during nighttime hours or for a few days until the cold front passes. Few of our Central Texas mammals truly hibernate. But some will go into the state of torpor when conditions require it. Extreme cold makes insects scarce. So most of the Mexican free-tailed bats who live under our bridges and in our caves head south to Mexico. But for unknown reasons, some choose to stay every year. And in what had been a relatively mild year before the 2021 Big Chill, it is thought that some returned early.
Bats don’t hibernate, but they are capable of entering a state of torpor for a few hours, days, or even weeks. A bat’s heart rate drops from 200-300 beats per minute to about 10 beats per minute. And the bat may go as long as 45 minutes without taking a breath. Their body temperature can drop to near freezing, depending on the temperature of their surroundings. A sudden drop in temperature below thirty degrees can cause the bat to freeze to death. But if the drop is more gradual, an internal alarm wakes the bat up so it can look for a warmer roost. However, moving roosts too frequently can deplete the food supply stored in the bat’s body. So while some of the many bats that died in Uri froze to death, it is thought that many more died of starvation or dehydration.
Like birds, mammals anticipate colder weather by growing thicker coats, adding a layer of undercoat, and putting on an extra layer of body fat. It’s December; look at your cat—is Fluffy recently fluffier? The old-timers always looked at the squirrels’ tails to predict the coming winter’s cold. And like our feathered friends, mammals can puff out to enhance the insulating effectiveness of their hair. When it turns extremely cold, mammals will hunker down in sheltered places to wait out the freezing temperatures. Raccoons and skunks sleep for several days when the weather turns extreme. But they don’t experience the physiological changes that come with hibernation. And animals who normally sleep in the day and forage at night may change their routine to take advantage of the warmer daytime hours. That’s why after a few freezing nights you might see a raccoon or opossum wandering through your backyard during daylight hours.
Because of their low metabolic rate and lack of fat stores, armadillos are intolerant of cold temperatures. And yes, they are ordinarily nocturnal mammals. But after several nights in the single digits, this one ventured out of its burrow in the middle of the day to search for a much needed meal of grubs, beetles, ants, termites, worms, and other invertebrates.
So what can we do to help our critter friends through the winter? The same things we do year round— provide food, water, and shelter. So plants whose seeds, berries, and nuts remain available when the weather turns cold are a plus—think yaupon holly, Ashe juniper, possumhaw holly, Texas persimmon, pecans…
In terms of water, keep the water sources you maintained all summer full. And here’s a neat trick should we have a hard freeze. Just place a pan full of hot water on top of your frozen bird bath.
Rethink “cleaning up” your landscape. When you look at that brush pile or thicket on your property, think of it as a place where your feathered and furry friends can shelter from the cold. Same goes for lower branches in that forested area. You may want to trim some lower branches to let in more light as a way to encourage the growth of understory, but leave some areas of low growth to provide wildlife with places to shelter from the cold wind. Hold off cutting those brown stems and grasses until early spring, and leave the leaves. Enjoy the eloquence of disarray!
Our Central Texas wildlife will use all their coping strategies in this winter’s predicted cold—migrating, hibernating, brumating, going into torpor, self insulating, huddling, burrowing, and brush sheltering. And if we all do our part, providing them reliable food, water, and natural shelter, they’ll survive to enchant us next spring.
We have finished up our fall HELM property visits and are now taking requests for visits in the Spring of 2023. If you would like the HELM team to visit your Hays County property to provide insights into how to provide for the wildlife on your property or help with other land stewardship concerns, go to https://beautifulhayscounty.org/helm/ and fill out our request form.