Feral cats can jump as high as six feet. Juvenile mice can fit through a hole smaller than an aspirin tablet. Stoats move so quickly they can scale an electric fence between high voltage pulses and land on the other side unscathed. We have learned these things by trying to fence these animals out.

We are fencing them out to atone for our mistakes. Human beings have rearranged the matrix of life on Earth, sometimes on purpose and sometimes by accident. In the nineteenth century, the British wanted to blow bugles and hunt foxes in Australia just like they did on their Yorkshire estates, so they shipped some over. The foxes still live there in vast numbers, devouring numbats and wallabies. Captain Cook accidentally left rats on tropical islands throughout the Pacific. Rats love nothing better than the egg of a ground-nesting bird. Whalers and explorers like Cook often had cats on board to control the rats; many disembarked and discovered that naïve island birds made for an easier supper.

Invasive predators have contributed to more than half of all bird, mammal, and reptile extinctions. What can we do? We cannot herd together all the foxes and dispose of them. We cannot poison all the rats. Only very brave souls dare propose killing that most beloved of creatures, the cat. So we are beginning to fence in natural areas and fence out invaders.

In Australia, a new enclosure to protect native animals from hungry cats, foxes, and other invaders goes up every year, on average. Federal, state, and municipal governments, NGOs, local environmental groups, and even individuals erect them. Last year, a nonprofit organization completed the world’s largest, encompassing an area thirty times the size of Central Park. New Zealand, South Africa, and the United States have installed miles of predator-proof fencing. There are fences in the city and fences in remote deserts. There are fences to protect lizards and fences to protect snails. One fence crosses forty-two streams, with special gates to let fish in and out.

The predators patrol the perimeter of these enclosures, sniffing, waiting. A tree could fall and break a fence, someone might leave a gate open, a kangaroo could jump on the top rail and crush a fence section like a tin can. It takes less than twenty-four hours after a fence break for the rats to start streaming in.

II.

When I was a kid, I watched a lot of “bear shows.” That’s what my family called television shows about nature, like Marty Stouffer’s Wild America. At the time, Marty Stouffer was a celebrity among nerds, but his reputation isn’t so great anymore. PBS did an investigation and discovered that he staged a lot of episodes. Once, his team filmed wolves chasing and killing a deer. The animals turned out to be within an enclosure, so the deer couldn’t get out. A prey-proof fence, I guess.

Filmmakers still regularly trick wildlife into camera-friendly behaviors. They put M&Ms in the carcass of a dead animal and send in trained “wild” animals to find them. They pester wild animals until they do something interesting. (One team of filmmakers reportedly smeared Bengay cream on a beaver’s anus to get it to move around.) They rearrange footage to give it drama and a narrative arc. And they produce a lot of sound effects in the studio. In the right hands, a pair of gloves can sound like the flapping wings of a bird.

III.

Here are a few things technology currently allows us to know about a tagged wild animal without leaving the office:

Where the animal is at all times

How warm or cold the animal is

When an animal is pregnant or giving birth

When an animal is interacting with another tagged animal

When an animal has begun hibernating

When an animal has died

Here are a few of the tools we use to control invasive predators:

Artificial perfumes designed to attract specific predators

Poison bait targeted at specific predators

Traps powered by gas-fired pistons that can kill twenty-four times before they need refueling

Here are a few of the tools we’re working on for the future:

Drones that search out invaders and drop personalized doses of poison

Biosensors that detect the urine of an invader

Smart cameras that detect particular species

Genetic modifications that spread through an entire population to kill them off

IV.

A couple of months ago, I took my children to the zoo. We visited the rhinos and the zebras and the penguins. In a rare show of natural behavior, we saw a cheetah poop. But the most enduring encounter with wildlife we had that day, the one we still talk about, did not take place behind a fence. We had paused to eat lunch on a picnic bench, not far from a metal trash can. It was the kind with the lid you push inwards. Suddenly we heard a rustle in the can. A gray squirrel poked its nose out, the lid resting on its little pear-shaped head. It looked around, squeezed out through the gap, and dashed off, the lid flapping in its wake. The children shrieked with delight, and a moment later the squirrel returned. It scaled the can and once more disappeared inside. It came out with a French fry in its mouth, scanned the surroundings, twitched its tail, and scampered into the woods ringing the zoo. We watched it far longer than we had any of the caged animals.

Many of us desperately want to preserve the thing we call nature or wilderness. But because we’ve destroyed so much, it is a slippery business to save what remains. If we don’t erect predator-proof fences, the world will lose the rabbit-eared bandicoot, a marsupial rodent with giant ears and a long pink nose. And we’ll lose the Newell’s shearwater, a seabird that brays like a donkey and dives down 150feet to catch squid. If we dobuild the fences, we lose the luxuriant creative abandon that produced these creatures. We create a demonstration plot of what once was.

A demonstration plot is not enough. I believe it’s the uncontained riot of the natural world that speaks to us. We seek a glimpse at the machinery of life. We seek a sobering corrective, a rough estimation of what the world might look like without us. We seek an escape hatch from our incessant selves, an impartial space. The coyote eats the baby rabbit, or the rabbit gets away. Both of those things happen at one time or another, and one is not better than the other. A fence, by contrast, takes sides. It declares who can eat whom.

Maybe we can look to the animals outsidethe fence. So far, after all, they are winning. Free of electronic collars and our constricting good intentions, the garbage-eating gray squirrels and the invasive cats roam the places we ignore: the fringes of industrial parks, the back alleys of cities, the banks of polluted streams. They consume and defecate and propagate more or less unhindered. And evolve. Perhaps it is up to the animals we despise to sustain the unbridled quality of wilderness we seek.

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