Residents of the Phoenix, Ariz., metropolitan area are feeling very sorry for the bears that have wandered into town.

The poor creatures are hungry, because Arizona (like southwestern Colorado) is suffering from a very dry summer and natural food is scarce. They’re thirsty, too; their water supply may have been diverted to a golf course or some other startlingly green patch in the middle of the desert. And they’re lost, because the places they used to call home now house human beings instead.

Of course no one wants these bears killed, because after all, it’s not their fault that their habitat has been disrupted. Instead, most people believe, they should be relocated, so that they can live happily ever after without bothering their human neighbors.

Unfortunately, it doesn’t work that way. All the prime bear habitat is already inhabited, sometimes by bears and often by people. There’s no empty space out there, just waiting to welcome new ursine residents. And although we humans pride ourselves in being much smarter than the average bear, we can’t seem to understand that once they’ve visited cities — where a 30-gallon garbage can of bear food is placed behind every house — they’d really rather live there.

Bears aren’t dumb. Given half a chance, they’ll come back. And most of the time they have that opportunity, because there are fewer and fewer places wildlife officials can relocate problem animals to really place them out of conflict with humans. A bear transferred far from Phoenix or Denver may not be able to get home, but he’s likely to be able to find a ranch house or a vacation cabin. If he makes a nuisance of himself there, he’ll be dispatched permanently.

As Phoenix residents are learning, that’s a sad state of affairs, but it’s also a warning to all of us: The West is finite.

Once the land beyond the Mississippi seemed so limitless that it was given away free to anyone who’d agree to farm it. It didn’t fill up in a year or five; the frontier moved steadily westward for several decades, broken only by dashes into gold-rich areas. Even once all the available land was claimed, there remained huge tracts of land under federal management, and that provided refuge for wildlife disrupted by our attempts to fulfill our manifest destiny.

But those lands weren’t ignored; the concept of ‘multiple use’ mean that they hosted loggers and miners, grazers and recreationists. They, too, became more and more crowded. There’s still a lot of space out there, just not enough for all the people, all the bears, all the mountain lions, all the corporations who want to lay claim to it.

And now there is no more. There’s not a new frontier just beyond the horizon. Growth now means not expansion but infill, which is eliminating the little pockets that once sheltered large carnivorous mammals. We are quickly reaching a point at which those pockets are so few, and the corridors between them so treacherous for wildlife, that we will no longer have populations, only individual specimens.

There is only one alternative to killing them: providing habitat that will forever remain untouched by man. It’s called wilderness, and the very concept is an anathema to many westerners who believe the land is theirs to use.

The last bear to venture into Phoenix probably won’t be killed outright. As the animals become increasingly rare, they’re likely to be confined and viewed as curiosities. Then one day residents will realize they haven’t seen one for a while, a long while. They’ll have gone the way of the grizzlies in the San Juans, the bison on the plains. We might have saved a couple, and we might even regret eradicating them (although we hope the bears aren’t holding their breath for that to happen), but we won’t be able to reintroduce them, because we won’t have any place to put them.