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The Sweet Sounds of Spring 

"Come play in the water with me!" A male Pacific Tree Frog sings his heart out to his lady love(s). Photo by Jim Anderson.

"Come play in the water with me!" A male Pacific Tree Frog sings his heart out to his lady love(s). Photo by Jim Anderson.

Thanks to hearing device technology from Central Oregon Audiology, I am acutely aware of the cacophony of hundreds of male Pacific tree frogs in Central Oregon's irrigation ponds, decorative water features, and drainage ditches that are making their presence known to one and all. They are gleefully summoning their lady-friend partners to come join them before the competition beats them to it.

All winter long, both male and female tree frogs have been buried in a damp spot beneath the sandy soil, hibernating. The singing is designed to lure females to the pond to see what the ruckus is about. In spite of the cold nights—even when ice forms on the surface of the pond—males will clamp onto a female, fertilizing her eggs as they are laid.

Unfortunately, those eggs are often consumed by our native, rough-skinned newts, other amphibians, and worst of all - the non-native bullfrog. One of those guys or gals in the vicinity of a frog pond is the worst news possible; they not only eat the eggs, but the tadpoles and adult frogs as well.

Speaking of cold nights, Pacific tree frogs are uniquely suited to survive freezing temperatures. In their winter stupor, a frog's heartbeat is almost non-existent, and there's no need to breathe as they absorb oxygen and water from the soil in which they're buried.

While the brain is slowed down, the frog is kept alive and capable of functioning by a special chemical—much like anti-freeze—that keeps the water in their bodies a frozen mush instead of solid ice. In fact, 80 percent of their body can freeze to slush during hibernation, and they can still thaw and hop away in the spring, moving quickly into mating mode —even when the nighttime temperature drops to the lower 20s.

In fact, a small population of Pacific tree frogs that was introduced intentionally in a pond on Revillagigedo Island near Ketchikan, Alaska, seem to be doing well, in spite of the sub-zero winters in that neck of the woods. And I once found a tree frog alive in a frozen cow footprint, about six inches deep in the mud at Benjamin Lakes, out on the Sagebrush Desert.

These remarkable tree frogs make several different calls, under different conditions. In addition to the musical "crek-eek" we're hearing these nights, they also have a dry-land call, which sounds more like "creee-ee-ee-eeek." When the serenading stops, we'll know that mating season is over.

Back in the '50s, scientists called them Hyla regillia, but around 1986 some frog taxonomists put their heads together and decided because of this-or-that scientific detail, they'd change the genus name to Pseudacris (pronounced "sued-ah-kris").

But a band of herpetologists, including Ernesto Recuero, begged to differ, splitting the whole tree frog tribe into three distinct species. I suppose the fact these little guys range all the way from Southern Alaska south to British Columbia in Canada, south to Washington and Oregon, and all the way to Baja, Calif., had something to do with it. However, Amphibian Species of the World hasn't accepted the name changes officially, so here's the way it is as of today:

-Pseudacris regilla for the northern region (our area)

-Pseudacris sierra for the central region

-Pseudacris hypochondriaca in the southern region (Baja, Calif.)

As an adult, the Pacific tree frog grows to two inches from snout to urostyle (the bony rod forming the last segment of the vertebral column of frogs, toads, and related amphibians). Males are usually smaller than females and have a dark patch on their throats—a vocal sack—which is inflated when the male is calling. Tree frogs can be a number of different colors, including green, tan, reddish, gray, brown, cream, and black, but most ours are a shade of green or tan, with pale or white bellies.

The frogs have a variety of dark and spotty markings on their backs and sides and can be identified by a dark brown eye stripe that stretches from the nose, across the eye, and back to the shoulder. I've heard reports of rare blue ones, but being color-blind, I can't tell. Please shoot voucher photos if you find any with bizarre colors, and send them to me at jimnaturalist@gmail.com.

Pacific tree frogs change color seasonally to better camouflage themselves, and on the end of each toe is a round, sticky toe pad, or disk, used for climbing, sticking to surfaces, and as a lure. A tree frog will eat anything smaller than itself, often remaining motionless as potential prey moves its way. It can then wiggle its little toe like a lure, which works perfectly on beetles, baby mice, and crickets.

As a member of the aquatic and terrestrial life zones, the tree frog has been recognized as a "keystone species," in that it plays a vital role—like the keystone block in an architectural arch—holding the structure of its ecological community together. Please think of that the next time you hear—or see—those non-native, pestiferous bullfrogs anywhere near tree frog territory. And remember: bullfrog legs are delicious cooked in butter.

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