For more than 1,000 years non-native animals have called the forests of Hawaii home. But those animals -- pigs, deer, goats, and sheep -- are exacting a toll on the native flora and fauna, as well as the landscape, of Hawaii Volcanoes National Park, where officials are working to hone their strategies for removing the intruders.

Many of the non-native species represent chapters of Hawaii islands history: Polynesians introduced domestic pigs to the Island of Hawai‘i more than 1,000 years ago, and Captain James Cook brought goats to the islands in 1778, according to National Park Service records. "Axis deer were brought to the Hawaiian Islands from India in late 1867 as a gift to Kamehameha V," park records add.

Others arrived more recently -- mouflon sheep were introduced to the islands in 1957 -- while others were simply opportunistic; domestic cattle that wandered free and became feral from time to time find their way into the park.

Unfortunately, these and other species threaten to damage archaeological sites, trample sensitive soils, and impact or wipe out species that are listed either by the state or federal governments as threatened or endangered. For instance, wallows created by feral pigs turn into breeding grounds for mosquitoes, which have transmitted avian diseases (avian malaria and avian pox) responsible for the lost of native birds. Pigs also have eaten both eggs and goslings of the endangered nēnē, or Hawaiian goose

Native plants are uprooted and destroyed, too; in the mid-1990s several mouflon sheep browsed on Mauna Loa silversword, a federally listed endangered species.

While the park has relied for the past three decades on a management plan for combating these non-native species, the animals still are widespread. In the park's Kahuku unit, for instance, there are an estimated 1,000 mouflon sheep today, said Rhonda Loh, the park's chief of natural resources.

With hopes of developing a more successful strategy, the park now is updating its plan for managing non-native pigs, sheep, feral cattle, and goats. Through January 20 the park is taking public comments on four options for addressing the non-native species.

The preferred option at this point is to use a variety of methods, including shooting from teams on the ground and in helicopters and relocation, to greatly reduce, if not eliminate, the non-native species.
However, reducing the numbers could go more quickly if officials relied on a plan that used "lethal techniques and ... the use of fencing," the draft environmental impact statement for the plan states.

Ms. Loh said earlier this week that the park wants to hear which alternative the public would prefer be implemented.

"We put it as a preferred alternative, it would give us the most flexibility, but we’re really open to what the public's thoughts are on this," she said during a phone call. "It’s not set in stone.”

In the past the park has relied on park staff and volunteers shooting the non-native animals, as well as 4- to 6-foot-high fencing to keep the animals out of various areas of the park. In some areas park staff have run fencing from sea level to 9,000 feet in elevation.