Winter in the Great Northern Forests is not the best time to find reptiles and amphibians in the northeast, to say the least. Many of us who are fond of looking for these animals find other hobbies for the winter, in places where there is a thick cover of snow for months on end. Every species has its own strategies to survive the winter, so I thought it may be interesting to go over how some of the more well-known species in my area will be spending this winter.
Wood Frogs: Wood Frogs are one of a handful of frogs in the northeast that can survive being frozen and they overwinter under the leaf litter in the forest. Thanks to sugars they produce in their blood, they can survive their bodies freezing to about 23F (-5C) and one study in Alaska found that the frogs there could survive freezing to much lower temperatures. Air temperatures may plummet to far below zero, but the leaf litter topped with a thick snow pack insulate the frogs from otherwise lethal conditions. Winters with little or no snow coupled with bitter cold temperatures are bad news for Wood Frogs, as well as any other amphibians overwintering on land.
Northern Leopard Frogs: Northern Leopard Frogs cannot survive being frozen like some other frogs and protect themselves by spending winters underwater. Their overwintering sites can have flowing water or not, but the standing water that ices over sometimes suffers from oxygen depletion mid-winter, something called anoxia, so the frogs need to find a spot that is at low risk of oxygen crashes. Sometimes they will just rest on the bottom of the water, but they also hide under cover. One fascinating observation during a radio telemetry study of Spiny Softshells in northern Lake Champlain was made when divers had to retrieve turtles to remove their radio transmitters during the winter and discovered many of the turtles had Northern Leopard Frogs hibernating under their shells!
American Bullfrogs: Like Northern Leopard Frogs, American Bullfrogs overwinter underwater. While their overall wintering habits are similar to Leopard Frogs, there is one recent story of a local bullfrog that I found absolutely fascinating. In September 2017, as frogs were settling into their overwintering habitat, a resident found a bullfrog in their springhouse and opted to relocate the frog elsewhere on his property. The same frog, identified by pattern and a scar, was see in the springhouse again in October, so the owner took the frog for a 1.2 mile drive and released it in a pond. In November, the frog was back in his springhouse along with another bullfrog, a Pickerel Frog, and a Green Frog. Springs make great overwintering habitat for amphibians because they almost never freeze and oxygen levels are steady. This frog clearly knew what it was doing.
Painted Turtles: Painted Turtles are the only turtle commonly known for having two uniquely different winter survival strategies depending on age. Adults, which live in lakes and ponds, generally just rest on the bottom of whichever body of water they spent the summer and may burrow into the mud and leaf litter for additional protection. During that time, their metabolisms shut down by roughly 95% they do not need to breath surface air all winter, instead extracting oxygen through the skin lining the roof of their mouths and the inside of their cloacas (the non-technical term for this is “butt breathing”). Sometimes oxygen levels crash in their overwintering sites, which forces the turtles to get their oxygen from glycogen molecules stored in their own muscle tissue. The same process is used by humans during times of extreme physical exertion and the resulting buildup of lactic acid is what causes that burning sensation in your muscles. After prolonged periods, that would kill most animals, but Painted Turtles buffer the acidity by extracting calcium from their shells. As seen in the video below, Painted Turtles also occasionally move from spot to spot, even under the ice.
Hatchling Painted Turtles, which hatch in the fall, remain on land in their nests through the winter and can actually freeze almost completely solid during that time. Even cooler (sorry in advance for an upcoming pun), is their ability to drop below the freezing temperature of water without freezing through a process called supercooling. If they come into contact with an ice crystal while in a supercooled state they will freeze almost instantaneously. All in all, the hatchlings can survive being frozen as low as 25F (-4C) and can survive supercooling to as low as -4F (-20C). No other reptile can survive body temperatures that low.
Wood Turtles: Wood Turtles do not have the same super-abilities as Painted Turtles when it comes to oxygen depletion and freezing hatchlings, but like adult Painted Turtles, they must overwinter underwater. Because they need high levels of oxygen in the water all winter, they do not typically hibernate in lakes or ponds where there is a high risk of anoxia, instead overwintering at the bottom of pools in rivers and streams. The pools do not need to be very deep, only four feet or so, so long as the bottom of the pool is below the main current. Undercut banks and piles of debris in the water from things like fallen trees are very attractive to the turtles as they protect them from strong currents and give the turtles lots of places to hide during their roughly five month long winter rest.
Mole Salamanders: Mole Salamanders in the genus Ambystoma (a genus including Spotted and Tiger Salamanders) are named so due to their propensity to spend time underground in crevices, holes, and tunnels excavated by small mammals. Apart from the breeding season when these animals venture to the surface and migrate to wetlands, this is where the salamanders will spend most of their time, including the winter. Not a whole lot is known about what they do down there during the winter, but in their fossorial habitats they are at very little risk of freezing during the winter. If their bodies did freeze, however, they would not survive.
Mudpuppies: The winter is actually kind of a busy season for Mudpuppies. Fully aquatic, these animals never purposefully venture onto land and can be found in rivers, streams, and lakes. The early and late winter is when these animals breed and they will remain fully active all winter. Numerous observations have been made of Mudpuppies moving from place to place and even foraging in mid-winter. In lab experiments, when given a choice, Mudpuppies prefer colder water with almost no exceptions and are good to go so long as the water itself isn’t actually frozen.
Snakes: All of our snakes should be underground by now. Their preferred overwintering habitat varies by species, but the vast majority will be using crevices, rotten stumps, or cracks along building foundations to get comfortably below the frost line where they will remain all winter. Some, such as the occasional gartersnake, have been seen overwintering underwater, and other species sometimes find themselves in people’s houses (basement or attic mostly) where they usually either go unnoticed or unappreciated by their human cohabitants. Gartersnakes can survive being mostly frozen for short periods of time, but they are the only snake capable of that particular science trick.
Stream Salamanders: Stream salamanders, like Two-lined, Dusky, and Spring Salamanders do not need to travel far from their summer habitat to survive the winter. The fast-flowing water and spring-fed seeps they spend the summer in will not freeze in the winter and should maintain high levels of oxygen for these animals that breathe entirely by absorbing oxygen through their skin. Many of the salamanders will find places to hide for the winter deeper in the river substrate, but these salamanders are some of the few species of herp that can be found during the winter by gently turning stones along the edges of streams. Generally speaking, they should be left undisturbed through the winter, however, because even brief exposure to freezing air temperatures can kill them.
Every species has its own strategy for surviving the winter. Most do so by finding ways to avoid freezing temperatures or by supercooling. Some have figured out how to survive the freezing process itself. No matter how they do it, once the snow melts and the ice breaks up, these animals will spring forth from the hills and the mucky depths, and back into our lives once more.