Monday, March 22, 2010


Spring in the Pacific Northwest was made for amphibians. They flourish in cooler temperatures than reptiles, and they do best where it’s wet, so the cool, wet springs of this region are great for them. And because amphibians need moisture and are small and have many predators, most of them are active at night, so that’s the time to be out looking for them. Most amphibian hunters use a headlamp to keep their hands free, as amphibians are elusive little critters.

There is a moderate diversity of frogs in this area, some of them common. The most ubiquitous is the Pacific Chorus Frog (Pseudacris regilla), and it seems as if they can hardly wait to start breeding. Individuals are heard calling during warmer winter days, and the choruses really start up by February. Their ribbit call is known to all because so many movies are made in Hollywood, where the species is common. The call is first heard individually and then swells into a chorus, as more and more males head for the wetlands in which they breed.

The Western Toad (Anaxyrus boreas [formerly Bufo boreas]) was also one of the most commonly seen frogs in the Northwest, but this is one of the species that has declined greatly in recent years, as part of the Great Amphibian Problem. We don’t see as many of them as we used to, but they are still widespread. If you can’t find an adult, you may see masses of little black tadpoles swimming together in a mountain lake or a shore lined with toadlets that have just undergone metamorphosis in late summer.

The Red-legged Frog (Rana aurora) is the common native frog that looks like a classical frog – a long-legged jumper with smooth skin. It is most common in wooded areas with abundant ponds, where you may find its big floating mass of around a thousand eggs in spring. You have to have one in the hand to see the conspicuous red colors on the underside of the legs and body. In the mountains and east of the Cascades you can find two related species, the Cascades Frog (Rana cascadae) and Columbia Spotted Frog (Rana luteiventris).

The Bullfrog (Lithobates catesbeianus [formerly Rana catesbeiana]) is one of the villains in the amphibian story. Brought from eastern North America for culinary and sporting reasons, this species seems to flourish almost anywhere it is introduced. Unfortunately, it does so at the expense of other amphibians and other aquatic creatures. A virtual eating machine, a Bullfrog will take in anything that fits in its capacious mouth, and it has been implicated in the decline of some other frogs that share its aquatic habitat.

One of the most interesting things about Northwestern frogs is their silence. Anyone coming from the East is used to frog choruses with multiple species calling, one of the real thrills of a rainy spring evening in Massachusetts or Florida or Missouri. But our frogs don’t say much. Although some toads have ear-splitting trilled calls, ours makes nothing more than chirps. Red-legged Frogs call from under water and can be heard only at very close range. In fact, our only noisy native frog is the chorus frog. Of course the introduced Bullfrog has added much to our soundscape, its loud jug-o-rum resounding from warm-water lakes all over the region.

The Tailed Frog (Ascaphus truei) is another silent species - it doesn’t even have ears. It lives in rushing streams, where almost any sound would be obscured by the sound of the water. Unlike many other frogs, the males don’t attract females by their calls, but instead go looking for them. They also can’t fertilize the eggs in the standard way by depositing sperm on them, as the current would wash the sperm away. Thus the males have evolved an extension, but it’s not a tail!

There is still much controversy about what has caused so many frog species all over the world to become rare or, in some cases, extinct. A special kind of fungus called a chytrid (Batrachochytrium dendrobatidis) is heavily involved, as infestations of this fungus can kill off all the individuals of some species in an area. Fortunately, our Northwest amphibians have not declined as thoroughly as have populations of many tropical montane species.

Dennis Paulson


keatonwilson said...

Nice post Dennis! Great to see tailed-frogs on the list... I didn't get to see an adult this summer, but we saw a few larvae in some streams south of Glacier... very cool with their suction-cup way of staying put.

Shep Thorp said...

Thanks Dennis! The frogs were jumping all around the Nisqually Refuge today, Wednesday July 23 during a rain storm. On the old Nisqually River Dike, adjacent to the borough slough, we saw dozens of what I think were immature Bullfrogs possibly feeding. On of our birders found a Red-legged Frog near the Twin Barns. We also observed many Tree Frogs. We were surprised to see so many frongs, and especially so many plain green, Bullfrogs?, on the old Nisqually River Dike near the cut-off to the Nisqually River Overlook. -Shep Thorp