Smart Fences

"Our fences are designed to keep pigs out of the native forest....They were never intended to keep people out."

Mark White
Director of Maui Programs

By Jan TenBruggencate

A wildlife fence is not just a secure barrier; sometimes it must be a filter, letting some species through but barring others.

And sometimes it’s like a valve, letting feral animals cross in one direction — out of a preserve — but not back in.

The Nature Conservancy’s Hawai`i forest preserves employ diverse technologies to allow humans and hunting dogs to cross their fences, while preventing pigs, goats, sheep, deer and even cattle from getting through.

There are dozens of gates and step-throughs in fences across the state. They are installed as a matter of course along established trails, but in special cases, they are also deployed as requested by forest users, said Ed Misaki, the Conservancy’s Director of Moloka`i Programs.

Multiple Designs

The Conservancy’s crews and contractors have developed multiple designs that meet the different needs of the unique wildlife refuges around the state.

They need to be different because a low fence step-over that works fine for keeping out rooting pigs on Kaua`i may not be effective for Moloka`i deer that can jump a six-foot barrier. And a design that is effective for goats on Maui may not be adequate for Mouflon sheep on the Big Island.

“Our fences are designed to keep pigs out of the forest, and sometimes goats, Axis deer and even cattle. They were never intended to keep people out,” said Mark White, Conservancy Director of Maui Programs.

The Conservancy seeks to ensure that cultural practitioners collecting medicinal supplies or hula greenery, or maile pickers or hikers are able to gain access to its forested areas. But it particularly wants hunters to have access, since hunters are wildlife managers’ partners in reducing the impact of feral animals.

“Our systems are meant to be simple, safe and effective, without altering the integrity of the fence,” White said.

One of the newest step-over designs was recently developed by Conservancy contractor Stuart Wellington of Wellington Fencing Co.  It consists of wide metal steps with steel crossbars that function like a cattle guard does. Dogs and people easily walk across it, but hooved animals won’t.

“This is the latest design. It involves a bit more expense, but it’s worth it,” said Trae Menard, the Conservancy’s Director of Forest Conservation.

Thus far, it has only been used in the Alaka`i wilderness on Kaua`i, but it appears to be very effective, Menard said.

Dog and Hunter Friendly

On the Big Island, a system that looks like an A-frame stepladder has been successful, said Shalan Crysdale, the Conservancy’s Hawai`i Island Natural Resource Manager.  It takes hikers and hunters over the full height of the fence.

“We really didn’t want to compromise the height of the fence — we needed to keep that seven-foot fence. We contemplated a little trap door and some other designs, but we think this one works best to allow hunters, cultural practitioners and others through,” Crysdale said.

Many hunting dogs seem able to traverse the ladder system. But a few dogs are more acrobatic. “We have a couple of dogs that can climb a seven-foot fence,” he said.

Misaki said his crews on Moloka`i install fairly simple step-over designs that are still high enough to discourage unwanted access by feral animals.

“It’s real simple. We put two metal fence posts close together with a couple of horizontal bars for steps. You step up and hold the fence posts in each hand as you walk over,” Misaki said.

Among the primary purposes of fencing important natural areas is to allow the removal of destructive species like feral pigs, and to prevent their return from neighboring lands.  A unique fencing option used on Kaua`i involves a pair of gates that allows pigs to breach the fence—but only in a direction that takes them out of the preserve and into neighboring hunting areas.

On the remote Alaka`i Plateau, an automated feeding system uses corn as bait to attract feral pigs into an enclosure along a fence. Once inside the enclosure, the pigs find there’s only one way out — through a one-way gate into a public hunting area. It won’t let them back into the preserve.

“We know they work. We have game cameras placed on some of them, so we know that we have pigs using them,” Menard said.