(Photo: National Park Service)
This little guy is western chorus frog (Pseudacris triseriata). Two weeks ago, hiking by a marshy area in the foothills around sunset, I was serenaded by them. It is a sure sign of spring when you hear them!
They are common in ponds and swamps in the montane zone. If you were to make your way to a pond, you probably won’t see these little guys, but you certainly will hear the males, at least during the mating season in the late spring/early summer. They are tiny, only a little bigger than a cricket (or your thumbnail – google for lots of cute images of people holding them), but their loud, distinctive mating call – which sounds like “reeeeek, reeeek” – can be heard from up to a half mile away. Listen for their call especially in the early dawn hours, or as sunset approaches and into the night. Often multiple frogs will call simultaneously; the cacophony resembles a froggy chorus, as their common name implies. Their chorus is a major part of the mountain’s aural atmosphere during warm summer evenings. If you have the chance, relax on a rock and enjoy their song. A good place to hear them are the ponds on the way to Cub Lake in Rocky Mountain National Park, and the various ponds on Boulder Open Space.
If you get too close to a calling frog, they abruptly stop, and either dive into the water or hide under leaves or other debris. This secretive behavior, plus their diminutive size and their nocturnal nature, makes this frog very difficult to spot. Usually if you wait a few minutes and remain still, they will start up again. If you do by chance see one, look for the white stripe along their upper lip. Above that, from their eye to their front leg, is a darker stripe. These stripes lend themselves to another common name for the species, the striped chorus frog.
There is a lot of confusion which chorus frog lives in Colorado. There is a similar species, the boreal chorus frog (Pseudacris maculata) that lives north of here, from Wyoming and Montana into Canada. The two species are difficult to tell apart – the western chorus frog has slightly longer legs than its boreal cousin. And that’s about it – no wonder there is confusion! Even the Colorado Parks and Wildlife website contradicts themselves, mentioning one or the other (but rarely both) as Colorado residents in various articles and papers.
If you can’t get out to listen to them, Yellowstone National Park has a sound library with chorus frog calls (with a very cute photo of a chorus frog with an inflated vocal sac). They recorded boreal chorus frogs, but they sound identical to our local western chorus frogs.