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Feature Story
Empty Nest Syndrome
Page 4

The Overdose

In April 2004, just at the time of my visit to Hakalau, newspapers and radio stations in Hawaii began reporting that a conservation experiment on the Big Island had gone awry. Tonnie Casey, the biologist at Keauhou Ranch, a privately owned nature reserve near Hawaii Volcanoes National Park in the southeastern part of the island, had attempted the largest-ever aerial drop of rat poison in Hawaii, covering an area of about 800 acres. But rats had survived -- and worse, feral pigs had died.

The incident had happened months earlier, in late August and September of 2003. The federal agencies involved in permitting and monitoring the experiment -- the Environmental Protection Agency and the Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) -- had kept mum about the problem. The first hint of trouble came when representatives of Kamehameha Schools, the landowner, apologized to hunters for the deaths of the pigs.

Following that single clue, Patricia Tummons, editor of the monthly newsletter Environment Hawaii, pieced the story together from documents she obtained through the Freedom of Information Act (none of the biologists or bureaucrats involved would speak with her on the record). In an experiment designed to kill every rat in the test area, evidence of live rats was found nearly two weeks after the poison was dropped. In the same period, Tummons reported, 13 pigs died.

The Keauhou Ranch experiment was the first large-scale aerial drop of rat baits in an area also inhabited by feral pigs, and the result was a rude shock to the conservation community. Biologists had assumed that rats would devour the poison so quickly that none of it would be available for pigs to eat, and certainly not the hefty amounts needed to make a pig sick.

When the news broke, there were rumors that the bait might have contained too high a dose of poison, but an analysis by the National Wildlife Research Center laboratory, in Fort Collins, Colorado, showed that the pellets were 0.004 percent diphacinone, less than the regulation 0.005 percent. But Jack Jeffrey, who came to Keauhou Ranch to photograph the first day of the experiment, noticed a technical glitch affecting the helicopter bucket used to broadcast the bait. The bait was dropping too quickly, and the bucket had to be repaired twice. In her search of government documents, Tummons discovered a ground survey by APHIS staff which found that densities of bait were higher than they should have been -- in some places more than five times higher than the rate of spread reported by Casey, the Keauhou biologist.

Though laboratory tests had indicated that pigs should be little affected by diphacinone-laced bait, Jeffrey suspected even before the troubling experiment that problems might arise. In a study done in a corner of Hakalau in the late 1990s, researchers put out "gnaw blocks" made of the same combination of grains used in rat bait but without the poison added. The idea was to use consumption of the bait as a measure of rat migration into the area, but feral pigs developed a taste for the stuff and devoured the blocks in short order.

The EPA is now investigating the Keauhou experiment. In the meantime, no one there or at APHIS, the agency whose employees found the dead pigs and counted the pellets on the ground, will comment. Casey, who is no longer employed by Kamehameha Schools, claims that "if anything, we underdosed the area for rats."

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Map: Small World Maps

OnEarth. Summer 2005
Copyright 2005 by the Natural Resources Defense Council