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Frogs face the freeze in different ways

Mink Frog
Mink Frog

FrogsToadsTurtles_110810.mp34.52 MB

 Chel Anderson is a botanist and plant ecologist . She lives here in Cook County and joins us periodically to talk about phenology or what’s going on in the woods right now. Welcome back, Chel.

Anderson: Hello, Jay.
Well, with winter upon us we have talked about how some animals protect themselves from the cold. What about frogs, toads and turtles? They seem a little vulnerable.
Anderson: Amen. That’s what I’d be feeling right now if I was a toad or a turtle or a frog. So, let’s start with frogs that are in something we would call the terrestrial group of frogs. So, these are frogs that we’ve talked about before in our conversations that really spend most of their lives living in the woods or in marshes. But, they really don’t spend a lot of time in the water, except for the breeding season. So, these would include Spring Peepers, Chorus frogs, Wood frogs, frogs that spend a lot of time in the water during the early spring when they’re mating, because that’s when they’re going to meet their mates and lay the eggs. But, once that’s over, they move back into the forest. So, those frogs, they’re among the amphibians that are capable of actually experiencing freezing temperatures. We’ve talked about amphibians like salamanders that aren’t capable of that, so they use a different strategy. But, for these terrestrial frogs that I’ve mentioned and toads—American toads, Eastern Grey Tree frogs—they don’t need to avoid freezing temperatures, because they’ve developed physiological strategies to allow their body temperatures to drop well below the freezing point of water. And, to be very simplistic about it, what they are able to do is let water move out of their cells and freeze outside their cells, so that it doesn’t damage the cells. Those frogs and toads are taking refuge, though, both from potential predators who are still on the lookout for them. So, this would be weasels and foxes and even birds of prey that are still around. They are taking refuge in that wonderful leafy litter that has just come down out of the trees, or under the coarse, woody debris that has come down in the last big storm. So, they’re looking for places to get underneath the leaf litter or some kind of nice, hidden place where they get some protection from direct exposure to wind and things like that and where they’ll get also the benefit of a nice snow blanket eventually that will reduce their exposure to extremely low temperatures, you know, down to 40 below or the deepest cold. So, that’s what they’re doing, or they’ve already done, hopefully, because we’ve had enough cold weather that they should be there by now. So, they’re hopefully resting comfortably. In the case of aquatic frogs, which would include things like mink frogs and green frogs, leopard frogs, that really spend most or all of their time in the water, they have to use a whole different strategy. Because, they too, they cannot freeze. They are not adapted to freezing. So, they are going down to the bottom of the permanent ponds or lakes or streams that they’re living in and they are just kind of barely burying themselves in the fine silt at the bottom, or they might be wedging into the root mass of something in a marsh. But, it has to be a place where it’s not going to freeze to the bottom, so you need to have significant water above you or some water moving through, you know, in maybe a spring-fed situation where there would be water moving through that would keep that area from freezing. The reason that they don’t go deep into the mud or silt is that they need to be breathing oxygen from the surrounding water while they’re in their kind of torpid state. They are not moving around very much, but, if the need arises, for instance, if where they are the oxygen becomes depleted, they move around to a place that is more suitable. Aquatic frogs need to be able to have oxygen during the winter, and they can get it through their skin as long as the water stays open and the oxygen doesn’t become depleted, but they need to find just the right kind of spot. In the case of turtles, this would be another species of reptile that also can’t freeze, so our Snapping and Painted turtles are not capable of surviving freezing temperatures. But, turtles are different in that their oxygen requirements, because they can reduce their metabolism so dramatically, their oxygen requirements are much smaller than these aquatic frogs that we were just talking about. So, they will bury themselves up to three feet deep. If the sediments are that deep, they’ll bury themselves very, very deep and spend the winter hanging out in that deep muck resting the winter away.
Chel Anderson, botanist and plant ecologist. Thanks again for helping us understand what’s going on around us this late fall.
Anderson: You’re welcome.