Isle rats target
of poison proposal

2 government agencies want to
"broadcast" the poison to protect
native birds and plants

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By Diana Leone
Star-Bulletin

Several government agencies are looking to use aerial drops of rat poison to help protect rare and endangered native Hawaiian plants and birds.

Staffers with the U.S. Fish and Wildlife Service and the state Department of Land and Natural Resources hope to show that rat-killing with Diphacinone would be "effective in reducing rat populations in native ecosystems and that it's safe for human health and the environment," said Katie Swift, a Fish and Wildlife biologist who specializes in pest control.

The chemical already is the active ingredient in bait traps in remote wildlife protection areas, said Paul Conry, state Forestry and Wildlife program manager.

"The next step would be to go to broadcast applications."

The enemy includes the Polynesian rat, whose forebears probably hitched a ride on the first sailing canoes, followed years later by black and Norway rats stowed away on European or American vessels.

Nobody knows for sure how many rats are out there, Swift said.

"But when resource managers do trap for rats, they catch them in pretty high numbers."

Species vulnerable to rat predation include all endangered ground-nesting birds, including the moorhen, gallinule, native duck (koloa), Hawaiian stilt and the state bird, the nene. Some native plants and snails are at risk, as well.

The agencies that would have to approve the new method are the U.S. Environmental Protection Agency and the state Agriculture Department. Swift and Conry said it probably will be months before they have all their data ready to make the application.

If approved, aerial dropping of rat poison would intensify the battle against the non-native pests by natural resource managers.

Here's how it would work:

A helicopter would be used to spread marble-size pellets containing Diphacinone at a density of 10 pounds per acre. That works out to one 8-gram pellet per every 62 square feet.

A field study showed that within a few days rats would find and chomp down on the fish-and-grain-flavored snacks, Swift said.

"Rats apparently find it quite tasty."

In five to seven days, a second application would be made -- that being the fatal dose.

"It's extremely safe," Swift said of Diphacinone, noting that it is not as potent as the rat poisons sold over the counter at hardware stores.

In fact, Upjohn, the manufacturer, originally patented the chemical as a blood thinner for human cardiac patients in 1952, Swift said. The amount of poison in each rat-control pellet would be five parts per million. A human heart patient's normal daily dose would be the amount in 1.3 pounds of the mix that is proposed.

Even feral pigs should fare OK: A pig would have to eat one-third of its body weight in pellets in a very short time to get a lethal dose, Swift said.

"American agriculture uses about 20 million pounds of Diphacinone a year for controlling rats in crops from alfalfa to walnuts," and have used it for 50 years, Swift said.

Sugar cane and mac nut plantations have used it in Hawaii.

The aerial drop of even stronger poison "has being used extensively in New Zealand, and they've been very successful in their efforts to remove rats and mongoose predators," Conry said.

"New Zealand has achieved spectacular results," Swift said. "And in Hawaii we feel that time is really running out for many of our native species."