Alien Snake Threatens Pacific Islands

Article excerpt

The reproduction of endangered Mariana crows (Corvus kubaryi) is intensively monitored, nests are protected, and (when necessary) eggs or young are moved to the safety of lab conditions until they are less vulnerable to the threats in natural habitats. Barriers on tree trunks and judicious pruning of adjacent trees are used in attempts to exclude snakes from nest trees. Two birds unique to Guam--the Micronesian kingfisher (Halcyon cinnamomina cinnamomina) and Guam rail (Gallirallus owstoni)--are maintained at captive propagation facilities on Guam and in mainland zoos. Studies of these and other species, in captivity and on nearby islands, are underway to bolster our biological understanding of their behavior, reproduction, habitat use, and population biology.

Until the 1950's, the island of Guam, like many oceanic islands, lacked predatory snakes, but the abnormally high ship and air traffic immediately after World War II resulted in the accidental introduction of the brown treesnake (Boiga irregularis) from the Admiralty Islands in the South Pacific. The nocturnal, arboreal snake quickly spread throughout Guam, feeding on the island's lizards, birds, and mammals. As the snake grew in numbers, it reduced the populations of several native species and ultimately causing unprecedented changes in the ecology of the island.

By the 1980's, when the snake was identified as the cause of the declines in the native fauna, 10 of 13 Guam's native forest birds had disappeared, along with several species of seabirds and lizards. Other species were reduced to precariously low numbers. The mildly venomous snake also created other problems: causing numerous power outages when contacting high voltage lines; consuming poultry, pets, and other domesticated animals; entering homes and biting children; and invading cargo leaving Guam for other destinations.

The U.S. Fish and Wildlife Service and Guam's Division of Aquatic and Wildlife Resources have made an intensive effort to protect and recover endangered bird and bat species on Guam using a wide array of conservation techniques and strategies. These efforts have been supplemented by researchers and cooperators from other Federal agencies (U.S. Geological Survey, U.S. Department of Agriculture's Wildlife Services, U.S. Departments of the Navy and Air Force) and a host of cooperators from universities, zoos, conservation organizations, and other island governments. The severity of the conservation crisis led to the establishment of the Guam National Wildlife Refuge to preserve habitat and serve as a focal point for research and recovery.

Only recently have we gained enough knowledge about the many biological problems caused by the snake to begin controlling snake populations by protecting habitats rather than individual bird nesting sites. One experiment involving the removal and exclusion of snakes from 2.5 acre (1-hectare) forested plots in northern Guam has demonstrated the potential role of snake barriers in promoting the restoration of important habitat areas for wildlife recovery. However, much work is needed to solve problems of costs, durability, and application in order to protect the broadest spectrum of native fauna. Recently, such snake exclusion technology was used to facilitate the repatriation of 15 captive-bred Guam rails to a 22-ha area of forest habitat on Guam National Wildlife Refuge.

The predation pressure exerted by high snake populations resulted in the disappearance of most of Guam's native birds within four decades of the snake's arrival. …