The Brown Tree Snake (Boiga irregularis) was accidentally introduced to Guam in the late 1940s or early 1950s on U.S. military cargo. The native range of the snake is Northeastern Australia, New Guinea and some of the island around New Guinea. It is thought that the Guam snakes originated from the island of Manus, a small island in the Solomons.
By the late 1950s/early 1960s it was well known that Guam had a snake population, often referred to as the "Philippine Rat Snake". What was not known was the devastating effect this introduced snake was having on Guams native species, especially birds.
Not having evolved with a nighttime arboreal (tree climbing) predator, the native birds had no behavioral or physical defenses. As a result, birds began disappearing with the smaller species being affected first. By the mid 1980s, 9 of 11 native forest birds were gone from Guams forests. Two of these birds, the Micronesian Kingfisher and the Guam Rail, were found only on Guam (endemic) and to this day only exist in zoos. Guam's forests had become silent.
In addition to this, the snakes also cause many power outages (on average once every 3 days). Sometimes this is island-wide but more often it is smaller localized outages. This costs money in repair bills and lost business revenue. The snakes do this by crawling on the power lines or getting into the transformers.
Due to the loss of bird life, insect populations are much higher on Guam (many birds eat insects). Because many birds pollinate plants and spread seeds, Guam will probably exhibit vegetation changes in the forests. Guam is rightly termed one of the modern day eco-disasters.
In the CNMI the Brown Tree Snake is considered to be the number one threat to the native wildlife.