Into the Wild

Deep in the Tree Frog's Chorus


At last, I find a frog. It is spread-eagled in the shallow water like a lost toy. Its throat floats before it as round and sheer as a soap bubble, pushing its head up. It looks almost pathetic as it waits for the light to move along. My flashlight. I crouch to take a closer look.

It is just past the hour when the world loses its color: the sudden dusk of early spring. Rain squalls still soak the days, but the sun has been forcing its way onto the stage. I am being reminded that the green we count ourselves lucky to be around all winter can hardly claim the same name as the radiant green of new growth.

In the last two weeks the frogs — these are Pacific tree frogs, also called Pacific chorus frogs — have been building to a crescendo of nighttime noise. Then came four straight nights of hard freeze and silence and a solid half-inch of ice on the marsh every morning.

I was worried that the chorus in my cathedral of muck was strangled. But here on the first night above freezing, the frogs are back to singing.

The Pacific tree frog is our most vocal frog by far and common in any slow-moving or still water, particularly where fish and invasive bullfrogs are absent. They sound so familiar because it is the frog cast in Hollywood for any nighttime scene. They range from British Columbia to Baja, from deserts to grasslands to mountains to rainforests.

And they range widely in color. The one I have spotlighted is richly rust-toned. Green morphs and brown morphs are typical, some with contrasting blotches on their backs. Then there are rare gray, red, gold, even blueish morphs. Think of a tree frog’s habitat. It moves between the fringes of ponds and grasslands — green — to rodent burrows and forest floor retreats — brown — and as spring turns to summer the world’s palette of greens turns to yellows and tans and there is no one camouflage that will best serve a small frog. Distinctive color morphs help hedge the survival bets.

One morph, it has been found, can change colors. It takes days or weeks for the change to occur and seems to be triggered not by the hue of its background but by its brightness.

The researchers who set out to use these frogs to demonstrate simple ideas about crypsis — an animal’s tendency to camouflage by choosing a background that matches its body — have returned from their observations scratching their heads. Brown frogs are no more likely than green frogs to be found in brown areas. Green frogs do not congregate in green areas. Diversity’s roots, it seems, run deeper than camouflage. Even color itself has hidden parameters. It shifts from week to week.

Sloshing, searching, farther up the marsh I find a brown morph. Maneuvering around it, I feel myself getting into deeper water and shine my light at my boots to see how deep. That is when the battery dies.

I’m left bodiless in near darkness. The chorus echoes around me. Faint lights from nearby homes brush the water, just enough for the corners of my eyes to inform me of phantom movements. I wait. The chorus strengthens. It resounds from up marsh, down marsh, and the flooded cow fields over a rise until it is a pure pulsing blue aurora of noise. My movements must have been quieting frogs for hundreds of feet around. Now, nearby, I hear individual rik-ik, rik-iks belted into the mesh of sound.

When a passing ambulance paints the distant highway red and white, its siren pairs well with the chorus. I can barely hear it.

In a chorus like this, male frogs place themselves at regular intervals. They call to attract mates. It is a taut net. The collective chorus brings females from far and wide. But when the females approach, each male wants to be heard as an individual. He will match the pace of his call but offset its timing from those of his neighbors. That is why, to our ears, the chorus has such a pulsating quality. You feel you’re always on the verge of catching individual notes. When you enter the net, I now know, you do.

Males are aggressive toward other males that come too close. There are special warning calls and postures and smackdowns. There are males that roam freely in hopes of chancing across a female. And then there are those that lurk like satellites just outside the awareness of calling males. Remaining silent, they attempt to intercept any female that appears.

The night is chilly and damp. I move slowly, worried that if water overtops my boots I’ll turn into a shivering mess — while all around me these small frogs are bathed in cold water with their skin so thin it offers no insulation. How could they have survived the freezes?

Tree frogs will retreat to shelter — under boards and logs, in rodent burrows — in winter and bad weather. Just a foot underground they are largely protected from cold and wind chill. But they have a more impressive survival skill as well, one fairly common in the world of insects but much rarer in vertebrates with only a few frogs and lizards known to possess it: the ability to survive the formation of ice within their bodies.

Antarctic fish stay alive in 28-degree saltwater by circulating antifreeze proteins in their blood. These frogs, however, can have up to 65% of the water in their bodies frozen and they’ll come back right as rain. Their eggs embedded in ice will still hatch. The liver is the key. When ice crystals begin to form in a tree frog’s body, its liver releases stores of glucose and glycerol that do not prevent ice but cushion cells and organs from damage.

The Pacific tree frog’s range includes alpine lakes and industrial stormwater basins. It is not surprising that it has life skills for many situations. How much more might we learn from it? Studies have been done on it in only a few scattered locations by a handful of observers dedicated enough to mark and track and interact with and assay individual frogs — which tells me that the amazing things we know about the species can only be a glimpse into the full diversity of links it has with the flow of colors and change around it, only a few rik-iks in the net it weaves on dark spring nights like this.