Science / Medicine : Guam’s Silent Enemy : This exotic exterminator--the brown tree snake--has caused a major ecological catastrophe on an island once filled with the sound of rare birds

On Guam, the tropical Pacific island halfway between Japan and New Guinea, a recent survey of hospital emergency room records reads like a horror show script.

Take, for instance, the case of a 2-month-old baby treated and released in March. Her father checked on the sleeping infant at 1 a.m. and found a 5-foot snake wrapped around her neck and chewing on her arm.

That same month, a middle-aged woman was treated for a similar problem. Her situation rivaled the shower scene in “Psycho”: She was sitting on the toilet when a snake, entering the house from the septic system, lunged out of the water of the toilet bowl and struck her where she least expected it.

Guam’s only native snake is a harmless, blind reptile that resembles an earthworm. But unbeknown to the military during World War II, ships carrying wartime supplies to Guam from Australia, New Guinea and the Solomon Islands also brought unwanted stowaways: brown tree snakes native to those areas that grow to 13 feet long.

Without the natural enemies like the predatory birds found in its native lands, the snake’s numbers on Guam have exploded to more than 6,000 per square mile, according to Thomas Fritts, a U.S. fish and wildlife specialist in reptiles. And in the space of a few decades, the snakes have eaten almost all of Guam’s birds.

“By the time we discovered there was a problem, the snakes were totally out of control,” said Fritts, who has been studying the snakes in an effort--fruitless so far--to control their numbers.

Because the brown tree snake is not highly venomous, most people quickly recover from bites. But doctors see only part of the problem caused by the reptiles. The agile climbers slither up power lines and short-circuit wires, causing frequent blackouts that cost Guam millions of dollars a year. Young snakes pop out of automobile air-conditioning vents and scare drivers; some of the island’s 121,000 residents have awakened to find the snakes in their beds.

But worst of all, the nocturnal snakes eat almost anything and can slither almost anywhere, including along branches where birds and fruit bats roost, into holes where lizards hide and deep into hollow tree crevices where many bird species once laid eggs unmolested.

The snakes’ victims include two species that existed nowhere else on earth, the Guam flycatcher and the Guam rail, both of which were once so abundant they were legally hunted.

“The whole time I was on Guam, I never heard a bird sound,” said University of Connecticut ornithologist Robert Craig, who is studying the bird life of the Marianas Islands, which include Guam. It was, he recalls, reminiscent of Rachel Carson’s book, “Silent Spring”: “not a song, not a sound.”

Of Guam’s 18 species of native birds, at least six have been wiped off the island since 1970; Julie Savidge, a University of Nebraska ecologist, has watched several of these species disappear during the course of her six-year study, while most others have become increasingly rare. “I was shocked at the decline,” she said. “This is an example showing just how rapidly extinction can occur and the devastating effects exotic species can have.”

Because of their tree-climbing, night-traveling habits, the snakes went mostly unnoticed for the first few decades after they arrived. But today they are so numerous and so widespread that “eradication is way out of reach now,” Fritts said. He estimates that in some areas, there may be as many as 12,000 tree snakes per square mile. “But control is possible,” Fritts said. “First, we have to learn everything we can about the snake to find its weak point.”

When Savidge began her study in 1982, no one really thought the snakes were a problem. No introduced reptile has been implicated in causing the extinction of a native animal. But that the snakes were at fault became quickly apparent as Savidge observed the secretive reptile’s night feeding habits: She found that the snakes eat birds, bird eggs, lizards and small mammals--even puppies, gripping them with powerful constricting muscles and then chewing on them until their flesh reaches the back of the snake’s mouth, where its venomous fangs lie.

Wildlife researchers are struggling for a solution. Savidge went as far as to pass out recipes for snake to people on the streets--sweet and sour snake, snake adobo --but they never caught on. Besides, Fritts said, the snakes are so numerous that even a bounty program probably won’t help.

Fritts hopes that further studies of the snake will yield an attracting chemical (to use in mass traps), repellent or fumigant. Eventually he hopes to establish some snake-free reserves for threatened species.

A few of the rails and kingfishers were removed from the wild before they became extinct and are now being bred in zoos in hopes of reintroducing them to such reserves on Guam some day. But at the moment, efforts are focused on preventing the snakes’ spread, like a malignant disease, from Guam to other islands.

Ornithologist Craig is particularly worried about the birds on the other 14 islands of the Marianas chain. Each island he’s visited hosts bird species found nowhere else. If the tree snakes arrived on these islands, he said, “the loss to science would be devastating.”

It’s not an unlikely scenario. Within the last 10 years, Fritts said, the snakes have shown up twice on Hawaii, and also on Kwajalein, an island 1,000 miles east of Guam, as well as Diego Garcia, an atoll in the Indian Ocean, and the islands of Saipan and Ponapi. All these snakes, which apparently found their way onto cargo ships, have either been killed or failed to establish a breeding population on these islands.

Fritts and U.S. colleagues have begun offering technical briefings at Micronesian and Marianas ports to teach inspectors how to look for the snakes in high-risk cargo like junk cars, lumber and government surplus property, where the snakes can easily hide. Such inspectors are already trained to look for agricultural pests and contraband, Fritts said, “but they aren’t trained to look for snakes.” No one envies them the job, “but somebody has got to do it.”

Some of the native island birds that are now considered extinct or near extinction: 1. The Guam broadbill 2. Bridled white eye 3. Guam kingfisher 4. Guam rail 5. Rufus-footed fantail.