Winter is Coming: How Do Frogs Avoid Freezing?

Yesterday while shopping at the mall, I noticed that some stores had already begun putting up holiday decorations. The racks were filled with sweaters and down coats. We humans (at least in the northeast U.S.) are preparing for winter. But what about our amphibian friends? How do they prepare for winter? After all, frogs would seem vulnerable to extreme cold with their thin skins and their need to constantly stay moist.

Actually, we don’t need to worry about the frogs. They are well-equipped to deal with the cold weather, even with Arctic temperatures.

Frogs are ectothermic, which means that they rely on their environment to regulate their body temperature. Birds and mammals, including humans, are endotherms. We generate heat chemically and internally by breaking down food. The bodies of ectotherms reflect the air, ground, and water temperatures around them. One advantage that ectotherms have over mammals is that they can survive for long periods without eating.

In the fall, frogs first need to find a place to make their winter home, a living space called a hibernaculum that will protect them from weather extremes and from predators. The frog then “sleeps” away the winter by slowing down its metabolism. When spring arrives, it wakes up and leaves the hibernaculum, immediately ready for mating and eating.

Aquatic frogs and toads such as the leopard frog and American bullfrog usually hibernate underwater in streambeds or on pond bottoms. Because aquatic frogs need oxygen, they lie just above the mud, or only partially buried in the mud, so they are near the oxygen-rich water. They may even occasionally slowly swim around.

Terrestrial frogs and toads typically hibernate on land. Those frogs and toads that are good diggers like the American toads burrow deep into the soil, safely below the frost line. Other frogs, such as the wood frog and the spring peeper, aren’t good diggers and so must scout out their winter homes in deep cracks and crevices in logs or rocks, or they might dig down into the leaf litter.

These frozen peepers and wood frogs might look dead; their hearts have actually stopped beating. But the partially frozen frogs aren’t dead. Instead, they have a kind of natural anti-freeze in their bodies. Ice crystals form in their organs and body cavity, but a high concentration of glucose in the frogs’ vital organs prevents freezing. When spring approaches and its hibernaculum warms up above freezing, a frog’s frozen body will thaw, and it will come back to life.

As you go about preparing for winter, think of the frogs with their amazing adaptations for survival, safe in their winter homes, waiting for spring.

Here’s a video from YouTube about the hibernation of a wood frog. It’s pretty amazing—take a look!

This is a partial repost of an earlier post from December 2010. Most of the information from the post came from an article in Scientific American, How Do Frogs Survive the Winter? by Rick Emmer.


Love Underground: The Shovel-Nosed Chamber Frog

We never stop being amazed by how amphibians are able to survive in the harshest environments. The Shovel-Nosed Chamber frog (Leptodactylus bufonius), for example, lives in the dry subtropical or tropical shrublands or grasslands of Paraguay, Argentina, Bolivia, and Brazil, in areas that have only intermittent freshwater lakes, marshes, and ponds. But this frog has evolved many incredible adaptations for overcoming the challenges of living in these mostly dry conditions.

Going Underground

Unlike most frogs, Shovel-Nosed frogs don’t have ponds or other aquatic areas in which to lay their eggs. They have only the muddy remains of ponds that have dried up. So with their shovel-like noses, they dig a chamber in the mud and then top it with a mud cone. Because no water can penetrate these chambers, the frogs produce a foam nest from the female’s albumin secretions to keep the tadpoles moist. But there is no food in the nest—scientists believe the tadpoles metabolize their own issues for food. Then the frogs wait for a big rainstorm that will wash away the burrow and create a predator-free pond (like a vernal pool) for the tadpoles to grow in. But the story isn’t quite over. After the Shovel-Nosed frogs vacate their burrow, a local toad reuses it as a hiding place.

Take a look at this amazing video of the Shovel-Nosed frog by FROGS ARE GREEN friend Joe Furman. We especially like the frogs’ little mating wiggle!

About the filmmaker:

Joe Furman lives in Houston Texas. He is a lifelong animal photographer and makes wildlife documentaries, mostly about reptiles and amphibians. He is also an artist and cartoonist and father of one.

Like most kids, Joe was attracted to frogs and toads and caught and kept them as pets for awhile, but then would release them back into the wild. He had, and still has, a neverending curiosity about tadpoles and the life cycle of frogs. In his twenties he got the chance to go to Costa Rica to look for the Golden Toads. This event set the course of his life ever since. He has traveled around the world with different organizations to study, film, and photograph reptiles and amphibians, and other wildlife. The kid has never left him. He still love frogs!

Frog Moon Dance

Well, its a marvelous night for a moondance
With the stars up above in your eyes
A fantabulous night to make romance….

The BBC Earth News reported today that biologist Rachel Grant of the Open University has discovered amphibians around the world synchronize their mating activity by the full moon. The animals use the lunar cycle to coordinate their gatherings, to ensure that enough males and females come together at the same time.

Grant made her discovery while studying salamanders in Italy. She noticed toads all over the road during the full moon. She then collated her data with a 10-year analysis of the mating habits of frogs and toads at a pond near Oxford, England, and with data on toads and newts in Wales collected by colleague Elizabeth Chadwick from Cardiff University, Wales.

This knowledge gives researchers practical information–for example, they will know precisely when to close roads to avoid killing frogs and toads during the mating season. It’s also useful information for FrogWatchers.

Now enjoy this video and imagine a romance—an amphibian romance, that is.