A few weeks ago Delaney stood on his 7,600 acres of land and watched hundreds of deer bound over his fences. The barbed wires keep his cattle in, but Delaney was also keenly aware of the problems they caused the deer. Obviously, before the study came out, Delaney knew deer liked his property, but he had no idea it was part of a corridor for thousands. Armed with the corridor study, last year the Wyoming Wildlife Federation reached out to Delaney and said they’d found funding to replace his fence. So far, five miles of fencing on Delany’s ranch has been lowered to 40 inches so deer can easily clear it as they jump, and the bottom wires raised to more than one foot, so young deer can slip below. “We’re in their country, right,” Delaney told me, meaning the deer’s country. “This is an opportunity where we can significantly lessen our impact on their turf, and it gives us the upgrade for our fences.”

Everyone wins with fence replacement, and that’s all fine and good, but this requires willing participation on behalf of private landowners, and not everyone is as receptive as Delany. Replacing fences is also expensive. It has cost about $25,000 a mile to replace Delaney’s fence. And although his required a bit more work than average, a similar project in the same Wyoming county to replace 45 miles of fence is expected to run more than $600,000. These expenses have been raised by the collective of nonprofits working to save the corridor, which most likely only happened because of all the attention the Red Desert to Hoback trail received.

Now, consider the great gains made in the past two years for the mule deer, and consider that optimistic estimates of the challenges ahead (if progress continues as it has) will still take years, perhaps a decade to resolve. Of course, there are hundreds of other migration corridors, some known, many more still in need of mapping, all across the West. Realize that deer, elk, moose, pronghorn, and antelope all depend on the ability to move north and south as seasons change, and that humans are still procreating and building roads and homes. Migration for ungulates will only become harder. What will happen in the future, Hall Sawyer, the biologist who discovered the Red Desert to Hoback corridor, told me, will be similar to what happens after a gory car crash: triage.

“The ideal is you throw that map out and say, ‘Hey let’s try and protect all this,’” Sawyer said. “But in private landscapes and multiple-use land that’s not really an option.”

Biologists hope to map more of these corridors in the same way they have the Red Desert to Hoback path, and surely some will be saved, thanks to the breakthroughs made by Sawyer and the Wyoming Migration Initiative. But some will fade out. It’s likely many herds, never fully understood, will vanish. By the end of December, the mule deer will finish their journey and arrive in the Red Desert, where they will spend the winter surviving on what little vegetation they can scrounge beneath the snowpack. This is a relatively new end for the herd, because here they’ll run up against the four lanes of Interstate 80, completed in 1986, built before anyone knew it would forever alter the trail of the mule deer.