I was walking all the way around my adopted hometown of Portland on the 260-mile-long "Urban Growth Boundary," Oregon's famous experiment in progressiveness and pissing off landowners. I passed farms, suburbs, pod-malls, vistas. But I was looking for something harder to see -- what a city was, or could be. I had come North to escape the desolation of Los Angeles. I wanted to know.

And then I heard it: a single breathy note, echoing down from fir trees along a two-lane south of downtown. A vibration pure as a flute but buzzed with unexpected harmonics -- near, like it was inside my body, and yet alien -- wet, dissonant, warning, welcoming: it was the roundest, interestingest sound ever.

An Explorer rushed by, vanished. A minute passed. And then another note, oddly chosen, filled the tall green space. Filled me. Then another, again at an interval I couldn't figure: Random? Augmented seventh? Twelve-tone row? Caged, uncaged, waiting in wealthy silence for the next note, I thought, Maybe this is what a musician knows: A single note can be the world.

The varied thrush -- it was a bird I remembered. Imperfect naturalist that I am, I had believed it to be found only far up in the North Cascades, where I'd first heard a pair fluting at each other in a grove of huge shaggy hemlocks, a sound so remote and antique it was unnerving. And here it was on the edge of town! My bird books say the varied thrush winters throughout the Pacific states, even down into my old California ranges. A rarity only to me, it seems.

But the books will have to be revised. The thrush is leaving.

Like hundreds of other birds, this one is moving its winter range northwards as the climate warms. The Audubon Society has just released a 40-year comparative study of 305 bird species showing an average winter shift of 35 miles, while some (like the varied thrush) have moved two, three, even four hundred miles. It's an unmistakable trend. Yet, oddly, a few species have moved south. Apparently global warming means global weirdness, eddies and unpredictabilities. Who knows what an Oregon winter is, any more? Surely not the snowy, sunny thing we had this year. Where's the drizzle? Soon we will add: Where's the thrush?

Only last year we heard that horticultural "plant hardiness zones" had migrated north one full zone since 1990. The National Arbor Day Foundation's Web map shows an eerie animation of all 10 zones, colored like snowcones, melting northwards -- Atlanta's milder winters drifting up to Knoxville, St. Louis' to Cedar Rapids.

The birds follow.

When I saw the varied thrush marked on a map of the 20 species shifting the farthest, it felt strangely personal. Turns out its winter range used to be centered right here on the Columbia River -- my paradise, my carpetbagging heart's delight. Now it has moved up to about Vancouver, B.C. It's the kind of bird you generally hear but don't see, but just a month ago I glimpsed one in a still-bare oak down by the coast. Colorful against the gray sky, orange and black but scruffy, like a mussed-up robin crossed with an oriole. I better put that date in my notes.

I came North to escape desolation: the heat, the sprawl, the juggernaut of loss. Now the south comes after me. And the thrush heads to Canada, like my lefty friends. I considered moving on, too, when it looked like torture and propaganda had become the new baseline of our political lives.

But there is no haven; there never was. Solzhenitsyn's generation sometimes spoke of internal exile. It didn't mean being sent off to camps. It was the silent inward withdrawal to a place of untouchability -- the last defense.

I wonder how much numbness, how much internal exile, will tempt the next generations, those to whom the scale of our global misdeeds will be unmistakable. To get through the next hundred years we will need to listen very quietly, even as we go about our arguing and living. We will have to look for something harder to see than guilt, harder to hear than slogans of hope or denial.

Sometimes I glimpse a way of living that isn't merely sprawl and avarice -- a city humbled by limits but edged by beauty, penetrated by it. There are moments so replete no desolation can touch them. We may go looking for them, but in truth they find us as often as not. If we are listening. 

David Oates writes about nature and urban life from Portland, Oregon.