The U.S. Army plans to dump rat poison from helicopters over Mount Kaala on West Oahu to quell the infestation of rodents that threaten the rare elepaio bird, also known as the monarch flycatcher. 

The Army is accepting public comments on the proposal until Sept. 7.

Efforts to control the rat population in the 1,764-acre Lihue Management Area on military-owned land in the Waianae mountain range have been going on since 2001. But the rat population has continued to grow while the elepaio dwindle in numbers.

Paul Smith, a biologist with the natural resources program of the U.S. Army Garrison in Hawaii, estimates that there are between 1,200 and 1,400 elepaio left on the island. Since this species of elepaio only live on Oahu, they are the last in the world, he said.

The elepaio were important to Hawaiian canoe makers, who believed the bird could help them choose the right wood for new canoes.

elepaio from DLNR pdf.
Only an estimated 1,200 to 1,400 elepaio, also called monarch flycatchers, remain on Oahu. courtesy of State DLNR

The Army used to set baits and traps and spread the poison by hand.  But according to the Army environmental documents, those efforts aren’t enough to keep the rats at bay.

“Everything we’re doing isn’t enough to keep these rats under control,” Smith said. “We aren’t getting enough control.”

Smith said the new method to poison the rats won’t be replacing their other baits and traps; it would just be an addition to what is already being done. The Army also says the poison shouldn’t affect other wildlife in the area.

Marjorie Ziegler, director of the Conservation Council for Hawaii, said she supports the drop.

“We trust the motives and the expertise of the Army environmental people and saving the critically endangered elepaio is important for a group like mine,” Zeigler said of the Waianae plan. “If you use it successfully, the short term potential impacts are outweighed by the long-term benefits.”

But she acknowledged those tactics are controversial given public concerns about the use of pesticides and other chemicals.

Zeigler said she has spent a lot of time on Facebook arguing about the merits of using rat poison on Lehua, a small island off of Kauai that’s home to seabirds.  The state Department of Agriculture approved a permit Tuesday allowing rat poison to be dropped on Thursday.

Zeigler also supports the Lehua effort, but opponents are worried about potential unintended consequences. The state Department of Agriculture says it plans to monitor the impacts both during and after the poison is applied.

Eradication Strategy

On military land in the Waianae mountain range, the helicopters will fly through the mountains while the buckets distribute the poison in 70 meter swaths, the proposal states. The management area is currently fenced off to stop larger mammals like pigs and goats from entering the area.

For every 2.5 acres, the helicopters will dump about 11 to 13 kilograms, or 24 to 30 pounds, of poison for the first application. A second dose of the same amount would need to be administered about a week later. Each application should take about two to four days, according to the environmental findings.

The Army will be using diphacinone and diphacinone-50 to kill the rats. The poisons were used in 32 other rodent eradications on the island, and neither of chemicals stay in the soil for longer than 60 days.

The Army expects to begin applying the poison in November, which coincides with the end of the strawberry guava season and the beginning of the breeding season for elepaio, Smith says.

Rats rely on the fruit to survive and multiply, and in the absence of the strawberry guava, they turn to feeding on the nesting birds, he said.

The poison wouldn’t hurt the elepaio, the environmental documents states, because those birds only eat insects and spiders. Smaller birds like finches or sparrows might be harmed if they accidentally ingested some of the bait, but Oahu’s larger birds of prey like owls would need to consume about 81 pounds of poisoned rat meat to feel any effects.

As for the birds that feed on insects and bugs, they would need to eat 5,000 pounds worth of invertebrates to get a lethal dose of rat poison.

Since the Lihue Management Area is closed to the public and hikers, the Army doesn’t expect any adverse health effects in humans from the rat poison.

Smith said the effort would only take place between November and the first two weeks of December. 

The Army may repeat the process in the future if it’s effective, he said.

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