When refuge manager Steve Hicks has to move 350 bison from winter to spring pastures at Fort Niobrara National Wildlife Refuge in Nebraska, he often uses herders on horseback, though ATVs are safer, easier and less labor–intensive.

When shrubs encroach on Okefenokee Refuge’s popular canoe trails in Georgia, staff members often send in crews with hand clippers, though chainsaws chew up swamp growth faster.

When Gerry McChesney airs plans to rid California’s Farallon Refuge of invasive house mice, the refuge manager cites several ways to protect gulls from rodenticide, though scaring the birds with sound and light has worked well in other island eradications.

In these cases and others, the easier, time–tested or more efficient actions are not off the table, but they’re not Plan A. That’s because the places in question are designated wilderness—areas where the Wilderness Act of 1964 intends man’s hand to be invisible, or nearly so.

To preserve wilderness character, refuge managers must show their actions are “the minimum require[d] for administering the area as wilderness and necessary to accomplish the purposes of the refuge, including Wilderness Act purposes.” What that generally means: no heavy machinery; no cars, trucks or aircraft; no easy–access roads or landing pads; no loud noises.

But rigid adherence isn’t always possible, even the law concedes. The trick for wilderness managers is knowing when to bend—and when to stand firm, despite the inconvenience.

In Nebraska’s 4,600–acre Fort Niobrara Wilderness, the choice of bison herding method may hinge on herd position. Horses are less intrusive. But four–wheelers can cover more ground and wield more clout. “Bison seem to respect a single vehicle pressuring them to move much more than several horses and riders,” says Hicks.

Herding bison on horseback also takes longer. “In an ideal world, that would be a good thing,” says Hicks, “because we could go slow and look at the habitats we are managing. Unfortunately, we live in a fast world where the duties are many, and time is short.” Still, he says, “we try to respect wilderness standards.”

In Georgia, managing the 350,000–acre Okefenokee Wilderness also involves tradeoffs. Hand tools suffice for some jobs—but not downed trees blocking trails or shelters needing quick repair.

Surveys of endangered red–cockaded woodpeckers that nest at Okefenokee also follow wilderness guidelines. Says biologist Sara Aicher, “With most of the islands accessible only by helicopter, we monitor every other year to reduce disturbance, and do not band the birds or install artificial cavity boxes,” as is common elsewhere.

Sometimes, the choice in managing wilderness is not whether to permit an intrusion, but how to deal with it.

That’s the case in the Farallons, where non–native mice have made the islands less hospitable to rare seabirds, including the ashy storm–petrel. The swarming of mice each fall coincides with burrowing owl migration. Instead of continuing their flight, the owls stay to feast—first, on the mice, and then, on the storm–petrels.

The proposed mouse eradication—which, if approved, could occur as early as fall 2015—involves potential wilderness intrusions, including mouse bait and the helicopters to drop it. Managers must also decide whether proposed gull–hazing techniques are the minimum necessary to protect the gulls.

McChesney concedes, “To eradicate the mice will involve some short–term impacts on wilderness character. But mice are having long–term impacts … because they’re affecting native wildlife of the islands. Our decision must weigh the short–term impacts against the long–term benefits.”

Susan Morse is a writer–editor in the Refuge System Branch of Communications.