SASEBO NAVAL BASE, Japan — The dead mice were laced with a common pain reliever — about one quarter of a child’s dose of acetaminophen each — and dropped Wednesday from a helicopter into the jungle canopy around Naval Base Guam.
The airdrop was a test of the newest weapon against one of the island’s most stubborn enemies — the invasive brown tree snake.
If the test goes well, the laced mice could prove to be one of the few effective ways to kill an unwanted and elusive predator that has laid waste to Guam’s ecology over the past three decades.
“The discovery that snakes will die when they eat acetaminophen was a huge step forward,” Anne Brooke, conservation resources program manager for Naval Facilities Command Marianas, said Thursday. “The problem was how you get the snakes to eat it.”
The brown tree snake was introduced onto Guam — which has no native snakes — by military transports following World War II. By the 1980s, the species had “eaten its way from one end of island to the other,” eliminating most indigenous birds, causing the extinction of some species unique to Guam, Brooke said.
Many still fear the snake could accidentally migrate again and cause environmental devastation on other Pacific islands such as Hawaii, she said.
Snake traps are set around military and civilian airports, and dogs are used to sniff outbound shipments of furniture and other cargo. But it has done little to reduce the problem.
Ten years ago, an offensive was opened against the snakes.
The U.S. Department of Agriculture, along with the Environmental Protection Agency, started researching ways to poison the tree snakes with commonly available commercial products. They provide a regulatory advantage because they’ve already undergone extensive testing, said Dan Vice, assistant state director of USDA Wildlife Services in Hawaii, Guam and the Pacific Islands.
After years of research, they discovered the household pain reliever acetaminophen was a deadly poison to snakes in small doses, and the EPA approved its use in Guam, Vice said.
Dead mice stuffed with the pain reliever were attractive bait. But there was still a problem with delivering the new poison to a species that spends most of its time in the forest canopy.
Ground traps, which were effective in some areas, were impractical in mountainous jungle areas where foot travel is difficult, Vice said.
Overcoming the snake’s terrain required a helicopter and a new paper delivery system.
Each mouse was attached to two squares of cardboard and a streamer of green paper. The streamer could be dropped from a low-flying helicopter and would catch in the upper tree branches of the jungle.
About 200 of the baits and some radio transmitters were dropped from a helicopter on 20 acres of Naval Base Guam on Wednesday as a first test of the system, Vice said.
“We’ve already found all the baits,” he said. “We will go out over the next few nights and find out their fate.”
The effectiveness of the drop will offer insights into how well it might work elsewhere on the island — and whether it might be a key to solving a longtime ecological problem, Vice said.
The USDA has a grant from the Department of Defense to expand the control efforts on Guam military bases in 2011. Eventually, Vice said, he hopes the method can be used islandwide in the near future.
“What we are doing now is finding out the hiccups in the system,” he said. “The next step will be 100 hectares (247 acres) of forest area on Andersen Air Base.”