Navy airdrops dead, drugged mice in battle with snake species

In its effort to rid the island territory of Guam of an invasive snake species, the US Navy has enlisted the help of an unlikely set of allies: Dead mice stuffed with a common painkiller.

The mice are stuffed with acetaminophen (known more commonly by its brand name, Tylenol), attached to little biodegradable "parachutes," and then airdropped into the treetops of Guam's jungle.

The idea is that the mice will be eaten by the brown tree snake -- a deadly species that was accidentally introduced to Guam after World War II and has since caused the extinction of several local species.

The dead-mouse airdrops, which began last month, are part of a plan hatched a decade ago by the US Department of Agriculture and the EPA to rid the island of brown tree snakes, reports Stars and Stripes. The drops are being carried out near Naval Base Guam by a naval helicopter crew.

"The discovery that [brown tree] snakes will die when they eat acetaminophen was a huge step forward," Anne Brooke, conservation resources program manager for Naval Facilities Command Marianas, told Stars and Stripes. "The problem was how you get the snakes to eat it.”

Ordinarily, packing dead mice with poison wouldn't work, because most snakes wouldn't eat a dead mouse, but the brown tree snake is an exception.

"There are very few snakes that will consume something that they haven't killed themselves," Dan Vice of USDA Wildlife Services told National Geographic. But brown tree snakes are scavengers as well as hunters, and that's the "chink in the brown tree snake's armor."

But simply dropping dead, poisoned mice into the jungle wouldn't be enough, because if the mice landed on the ground they would be eaten by lizards and other ground-level creatures, and not by the brown tree snake, which lives in treetops. National Geographic explains how this problem was solved:

Before the laced mice are airdropped, they are attached to "flotation devices" that each consist of two pieces of cardboard joined by a 4-foot-long (1.2-meter-long) paper streamer.

The flotation device was designed to get the bait stuck in upper tree branches, where the brown tree snakes reside, instead of falling to the jungle floor, where the drug-laden mice might inadvertently get eaten by nontarget species, such as monitor lizards.

To determine whether the dead-mouse drops are having the desired effect, some of the mice are equipped with radio transmitters that can be monitored for activity.

"If we go out tomorrow and the radio signal from the bait has moved, it's very likely that [it was eaten by] a snake," USDA researcher Peter Savarie told National Geographic.

Preliminary results on the project aren't in yet, but biologist Haldre Rogers of the University of Washington in Seattle says that, at best, it will reduce the snake population, not eliminate it entirely.

"Unfortunately, we don't have the silver bullet for brown tree snakes yet," she said.

A detailed description of the plan can be found here (PDF), courtesy of the USDA.