KAHANAHAIKI — Rats are a serious threat to native and endangered plants and animals in Hawaii. They prey on native birds, sea turtles and tree snails and consume seeds, fruits, flowers and plants.

The problem is so serious, with millions of rats on Oahu alone, that the U.S. Army could soon float an Environmental Impact Statement as a precursor to an “aerial broadcast” campaign. A bucket hung from a helicopter would be used to disperse rat poison across large swaths of inaccessible forest for the first time on the main Hawaiian Islands.

Steve Mosher, Elepaio and Small Vertebrate Pest Program Manager for the U.S. Army‘s Natural Resources Program, says there is no active plan to implement the campaign. The Army just wants to keep its options open. The idea — already used on the uninhabited islands of Mokapu off Molokai in 2008 and Lehua off Kauai last year — is merely in its infancy.

The Army says the main active chemical in the rodenticide — diphacinone — is a so-called first-generation blood thinner that causes excessive bleeding and eventual death for rodents that eat it repeatedly for days. It says the poison is safe for humans up to fairly heavy concentrations. Mosher says the pellets would decompose quickly in rain or sun into its base elements of carbon and oxygen and would not contaminate the water system or food chain.

The program would only be used in areas that are fenced off to keep feral pigs from eating the pellets directly. In 2008, the U.S. Environmental Protection Agency published its final risk mitigation decision for 10 rodenticides, including diphacinone, addressing the danger to non-target wildlife that eat the pellets or the rats that died from the poison.

The pellets could be spread by hand in smaller areas that are accessible to humans, like Kahanahaiki. The use of pellets would be seasonal, based on when endangered plants flower. The goal would be to keep rodent populations down long enough to allow the native species to prosper.

The Lehua rodenticide application in 2009 was rumored to be a potential cause of a massive fish kill that had residents of West Kauai and Niihau concerned, though testing failed to reveal any diphacinone. But because the Army recognizes that concerns about safety are bound to pop up, the public information campaign is starting early.

“The word ‘poison’ is scary, but rats are scary too,” said Oahu Army Natural Resources Program Environmental Outreach Specialist Candace Russo.

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