Rana Cascadae, Cascades Frog

Day 243: You might think that the "cascade" in Rana cascadae's scientific and common names (Cascades Frog) referred to riffles or waterfalls, but in fact it reflects a larger habitat: the Cascade Range. It inhabits higher elevations than the Red-Legged Frog, but in the transition zone where the species overlap, the two can be difficult to tell apart, especially if young specimens of R. aurora are present. Once you move above 4500', it is unlikely that you would find R. aurora. R. cascadae's vertical range extends to 6000', and is limited to a relatively narrow band including the Cascade Crest and Mount Rainier. Sometimes these frogs appear in great numbers and can turn their marshy habitat into a living obstacle course for anyone venturing into their territory. The drum-like reverberation of a human footfall may set the wetland springing as a dozen or more frogs leap to safety.

Where Ranges Overlap

Day 306: Where the ranges of two similar species overlap, it is always advisable to take photos from multiple angles in order to capture as many field characteristics as possible. This philosophy holds true for plants as well, but it is particularly important when trying to make the distinction between frogs. Two species occur between 2500' and 6000' with Cascades Frog (Rana cascadae) having a range of 2500' to 6000' and Spotted Frog (Rana pretiosa) from near sea level to 8000'. Red-Legged Frog (Rana aurora) also occurs up to 4700', but only rarely is found above 3000'. R. aurora was not a consideration in the case of this specimen from Ghost Lake at 4400' near Cayuse Pass, but the identification points discussed here will also help separate it.

It's often impossible to capture a froggie for examination and certainly not the method the frog would prefer. A few simple observations will allow the amphibian to retain its dignity while assuring the observer of a good possibility of a correct ID. First, does the subject have strong dorsolateral folds extending from immediately behind the eye and continuing to the hip? If distinct, you can rule out Spotted Frog. But suppose the object of your attention is almost entirely submerged in water? Note the orientation of the eye. Does it look out toward the side, or does it seem to have an upward tilt? Best determined by looking directly down on the frog in question, an upward angle denotes Spotted Frog and rules out the other two options. Likewise, presence of full toe webbing indicates R. pretiosa; partial webbing is present in both R. cascadae and R. aurora, but of course this requires a view of the toes.

Now it gets a little more technical. Often, Cascades and Red-Legged Frogs can be distinguished by the presence or absence of reddish pigment on the legs. D'uh! But since the skin of frogs contains photoreceptor cells which respond to light levels by changing colour over a protracted period of time, this is not always obvious. If observable, dark spots on the back will be distinct in Cascade Frog, somewhat blurry in Red-Legged, but these can be difficult to distinguish when your froggie friend is in "mud camo" mode. The colour of the tummy and throat can be helpful, but not alway. Absence of mottling distinguished Cascades Frog, but either species may exhibit varying degrees of mottling. Likewise, presence of a facial mask may or may not be easy to determine, but if it is distinct behind the eye and not speckled with light patches, your frog is R. cascadae. The light yellow, unmarked belly and chest on this specimen add to the evidence that it is a Cascades Frog.

There are other points to consider as well, and while it's always best to note each one, three should suffice in all but the most difficult situations. Happy frogging!

Camoufrogged

Day 262: Watching where you step is very important when you're searching for rare plants and the occasional Fungus of Worldwide Concern ("FOWC"). While glopping through the gloopy mud at the edge of a bog, I was mildly startled when several brownish-green blobs leapt for the safety of the denser forest. Although I'd had my eyes peeled for Cascades Frogs (Rana cascadae), I had not spotted them until they moved, and then they seemed to be everywhere. Fortunately, my footfalls set off vibrations in the soil well in plenty of time to alert them, but of course that made approaching one for a close-up all the more difficult. Still, sometimes stillness is the best adjunct to camouflage, and this fine froggy froze in place. I moved in slowly, careful to keep my shadow from falling on my photographic prey as I knelt down in the wet. When I stood up again, I noted how effective this species' markings are in making it blend in with its environment. Only the symmetry of the eye gives it away.

Reviewing What We've Learned

Day 180: All right, class, let's review what we've learned about frog species this week. And before you accuse me of using the editorial "we," let me remind you that I've been learning right alongside you, and now I feel more confident in my ability to differentiate Cascades Frogs from Northern Red-legged Frogs.

First of all, the most reliable field characteristic seems to be the spots on the back. Cascades Frogs have well-defined spots as opposed to those of Red-legged Frogs which have a blurred or somewhat indistinct outline. Cascades Frogs have yellow bellies and legs, but the observer can be misled by a young Red-legged Frog whose red pigmentation has not yet developed. Often, the red pigmentation isn't visible on the legs, but may be seen in a ventral view. Of course that means dip-netting your specimen and subjecting it to the indignity (however brief) of being turned over on its back. Unless you are engaged in a formal scientific study, I strongly advise against this. The next characteristic is a little more vague. Red-legged Frogs only extend in range to approximately 2800-3000 feet elevation, overlapping the range of Cascades Frogs in a wide band. With climate changes occurring, this range may move up, creating a broader area in which the two species may coexist.

The Cascades Frog shown in this photo was found at 3000' elevation, very near an area where Red-legged Frogs have also been sighted. However, I am happy to report that my initial assessment of its identification has been confirmed by two experts in the field of "frogology." Incidentally, Cascades Frogs were recognized as a separate species in 1939. The holotype specimens were collected in Mount Rainier National Park.

Confirmation Of Identity

Update: My expert and her expert got their heads together today over my photos of the frogs and egg mass, and I am happy to report that we are ALL in agreement on the identification: Cascades Frogs. I feel much better now.

When Experts Disagree

Day 178: I do not claim to know much about amphibians, so when I captured a portrait of a frog of unknown species, I referred it to an expert for identification. It wasn't the best photo as far as being a "field guide" shot. It failed to show enough definitive features, but my expert said she thought it was a Cascades Frog. She offered to refer it to another expert who reported back, "I think it's a Red-Legged Frog based on what we've observed previously in that location."

I'd like to point out something I learned early on in my career as a naturalist: never assume that your specimen is Species A simply because Species A is the most common in the area. My expert's expert's remark made my hair stand on end, an example of bad science if ever there was one.

Since my initial submission to the "panel of two," I have taken much better photos showing the full morphology of the frog in question, and just this evening referred them back to the experts along with this image of an egg mass. I offered my own observation and said that if I was wrong, I would appreciate knowing the points on which I failed. That said, at least I'll know I was in good company. One or the other of my experts has to be in error.

Advanced Frog-Stalking

Day 166: "Practice makes perfect." I'm getting better at this. Of eight or nine froggies visible from a distance of fifteen feet, I only spooked two as I clambered over the boulders surrounding their pool in the hopes of getting a "field guide" photo showing the full morphology. My success solidified what I had suspected: these are Cascades Frogs, Rana cascadae, as evidenced by the yellow belly and distinct black spots.

The Cascades Frog ordinarily breeds from April to June. However, I observed a large mass of eggs in which the tadpoles were already clearly visible. According to the Washington Herp Atlas, breeding begins when water temperatures reach 46° F. This species breeds in still or slow-moving water. The larval period lasts two months. Adults may measure as much as three inches in length from snout to vent. Cascades Frogs can be found at altitudes of 2000' and higher, above the upper limit for the Red-Legged Frog. There have been no reports to indicate that this species is in decline, and from what I observed on this occasion, there are likely to be many more generations of Rana cascadae to come.

Frog Stalking 101

Day 158: Not far above the point where the Westside Road crosses Fish Creek, the road takes a sudden dip where an old culvert collapsed during one of Tahoma Creek's many flooding tantrums. A trickle of the creek still flows there in the early season, its progress slowed by accumulated rock and sand. At present on the high side of the slump, there is a small pool, not much bigger than a bathtub (if not as deep), and as I approached it on my walk, I noticed ripples on the surface. As I got closer, I saw what I took to be a fish tail disappearing into a hollow beneath some rocks. "Sculpins," I remarked aloud as I walked past. "It's gotta be sculpins."

On the way back down the hill an hour or so later, I thought I'd try to sneak up on them, camera at the ready. Well back of the site, I slowed my pace and started inching forward with a soft and irregular gait. If you've read Frank Herbert's "Dune," my technique could be likened to that used by the Fremen in crossing the spice desert without awakening the sand-worms...step, drag, drag, step, step, wait, drag, step. At ten paces, a splash informed me that my stealth skills needed additional work. And then I spotted something which was not a rock. Neither was it a sculpin, as I'd supposed. I snapped a few long zoom shots for documentation purposes and then, risking all, began edging toward my quarry for a closer portrait.

I won't claim this as a testament to my frog-stalking ability, but rather will attribute it to the braveness of my little friend. I could not capture enough field characteristics to identify Froggus cutus due to the light on the water surface, but if you look carefully, you can see his little feet and hands.

Footnote: I referred Froggus cutus to an expert for identification: Rana cascadae, Cascades Frog.