74: Wood Frog

I write to you from Arapahoe, Ute, and Cheyenne land. I am interested in learning about the different animals that live in the place where I was born. Before we start with today’s animal, I want to emphasize that biological classification as understood by western society has its roots in racism, sexism, and transphobia – here’s a good explainer about why.

Even though we’re heading into winter right now, you can listen to the sound of wood frogs (Rana sylvatica) and hear the sound of spring arriving, as these frogs wake up from their winter hibernation. Back on animal #56, we talked about the Northern Leopard Frog and its hibernation habits – get down into water, at the bottom of ponds and streams, that never freezes, and wait out the winter. If the water somehow does freeze, the Leopard Frog will die. Fascinatingly, the Wood Frog does something completely different! They live in shallow, ephemeral ponds that either completely freeze or simply disappear in winter. Instead, they excavate a burrow into the soil and then freeze – their heart stops, their blood stops, and ice forms beneath their skin. Their body produces higher levels of glucose to prevent damage to their organs during this time.

Wood frogs in Colorado are a fascinating remnant of the last Ice Age. Most of their range is further north than Colorado, and they even inhabit parts of Alaska. Approximately 11,000 years ago, the vast ice sheets of the Wisconsin Glacial Episode made their final retreat. In Colorado, that glaciation period is known as the Pinedale, a period when glaciers whose remnants linger today marked much of the mountain landscape. This was especially true in the area that is today Rocky Mountain National Park (and you can see a cool map of where some of these glaciers were here). When these glaciers were growing, vegetation zones shifted southward ahead of them with their accompanying fauna; when they retreated for that final time, wood frogs remained behind in the high, cool, wet environments where they could thrive. As a result, the only wood frogs in Colorado live in isolated relict populations in the Medicine Bow-Routt National Forest which includes my favorite named mountain range, the Never Summers.