Ka'u rat-control program halted after deaths of feral pigs

By Jan TenBruggencate
Advertiser Environment Writer

Kamehameha Schools has halted its rat-control program in the forests of Ka'u on the Big Island after a dozen pigs died last year from eating poisoned bait.

Officials said it was the first known case of feral pigs going after rat bait, and the first known Hawai'i feral pig fatalities from the chemical diphacinone.

Rats are considered one of the primary threats to native birds and plants in the Hawaiian forest because they eat eggs, chicks, seeds and seedlings.

Hundreds of rats and mice were killed in the same period as the pig deaths, according to landowner Kamehameha Schools.

Diphacinone is a blood-thinning, or anti-coagulant, compound sometimes used in human medicine. It acts much like the more familiar rat bait warfarin.

"Kamehameha Schools regrets the inadvertent loss of the pigs in this situation. While we do work with the local hunting community to control wild pig populations on our land, our target in this case was the rat," said schools Hawai'i Island region manager Robert Lindsey.

Studies with domestic pigs had suggested the animals were tolerant to the chemical and not at risk, the schools said in a press release.

The landowner said it had been controlling rats in the area with bait traps for about 10 years without any pigs breaking open the sturdy plastic traps anchored by fence posts and 2-foot-long ground spikes.

In a test in August, the schools distributed fish-flavored diphacinone bait aerially on about 750 acres of forest in addition to bait traps. The U.S. Environmental Protection Agency approved the test.

"We think the pigs got a taste for the aerial bait, and then went after the bait traps," said wildlife biologist Tonnie Casey.

Reach Jan Tenbruggencate at (808) 245-3074 or at jant@honoluluadvertiser.com.