The snakes are believed to come from Guam where they were accidentally introduced in the late 1940s or early 1950s on U.S. military cargo.
The native range of the snake is northeastern Australia, Papua New Guinea and some of the islands around PNG. It is thought that the Guam snakes originated from the small island of Manus in the Solomons.
By the late 1950s and early 1960s, Guam was already referring to the species as the “Philippine rat snake.”
What was not known was the devastating effect the snake was having on Guam’s native bird species.
Not having evolved with a nighttime arboreal or tree climbing predator, the native birds had no behavioral or physical defenses.
As a result, the birds began disappearing. By the mid-1980s, nine of 11 native forest birds were gone from Guam’s forests. Two of these birds, the Micronesian Kingfisher and the Guam Rail, were found only on Guam and now only exist in zoos.
The snakes also caused many power outages, an average of once every three days. This costs money in repair bills and lost business revenue. The snakes caused this by crawling on the power lines or getting into the transformers.
Biological characteristics
The brown tree snake has a vertical pupil, rear fangs, a large head in relation to the body, and a brownish or greenish color. Sometimes faint bands can be seen on the body. The coloration and the bands can be somewhat variable.
The snake is about 18 inches long after hatching. Adults are generally 4 to 5 feet long and as big around as an adult human’s thumb. On Guam snakes in excess of 9 feet have been captured. Juveniles, up to about 3 feet in length eat lizards exclusively. Adults switch over to warm blooded prey, rats, mice, shrews, birds and bird eggs.
Females can lay up to 14 eggs it is believed. On Guam the snakes can probably breed year round. It is not known if females can lay more than one clutch per year. The eggs hatch in 90 days. The snakes are around 3 years old when they first reproduce. Females can probably store sperm for several years. Meaning they can mate with a male, lay fertile eggs and then lay another fertile clutch of eggs 2 years later from that same male. This has been documented in zoos with other species of cat-eyed snakes.
Catching snakes
There is an effective trap in use for brown tree snakes. It consists of a mesh cylinder with one way opening flaps on each end. The snake can get in but cannot get out. To entice the snake into the trap there is a live mouse inside. The mouse is in a wire mesh box so that the snake cannot kill the mouse once inside the trap. The mouse must be fed on a weekly basis. This makes trapping very labor intensive. Never the less, this trap is used extensively on Guam around the sea ports and airport and Guam’s Division of Aquatic and Wildlife Resources is using trapping to clear large areas of jungle of snakes. We use these traps on Saipan to hopefully capture snakes that have just entered or to locate a rising snake population.
The following are the numbers of trap set up for brown tree snakes:
Saipan — 150 in port areas. Presently traps are being focused into one area near seaport and the airport.
Tinian — 30 at seaport.
Rota — 30 at seaport.
Despite all of the effort and numbers of traps, there has never been a snake captured in a trap here on island.
There are probably several reasons for this which include:
Low snake numbers. There are just not a lot of snakes here, which is good (no complaint about this). On Guam any patch of jungle, no matter how small, has an excellent chance of harboring snakes.
Abundant prey base. The bait mouse in the jungles of Guam is about the only warm blooded animal in the area. For the snakes this stands out like a beacon. In the CNMI there are still plenty of birds, rats, mice and shrews. All of these smells and sights take the snakes attention away from the mouse in the trap.
Low snake movements in relation to the abundant prey base. The snakes do not have to move much to find something to eat. This reduces the likelihood that a snake will come in contact with a trap during its normal nightly movements. On
Guam studies have shown a great deal of snake movement. They are constantly moving through the jungle searching for food. This increases the odds of a snake running into a trap. Snakes on Saipan probably do not move as much.
Maintaining the bait mice are the major limiting factor in medium to large scale trapping programs.
28-SNAKE
The brown tree snake program actively works to prevent the introduction of this invasive species to the islands. Personnel and inspection teams are located on Tinian, Rota and Saipan. Saipan houses a kennel where dogs are trained to locate brown tree snakes. The port of Saipan is also installing a quarantine area for vessel shipments (boats and cargo) that have the potential for unknowingly transporting snakes. CNMI brown tree snake.
All contractors doing major construction, excavation, or earth moving are required to have a free inspection of their site and equipment by DFW’s BTS staff. Contractors are also required to have their workers participate in a brief on-site snake prevention training workshop provided by DFW. There is no fee to the contractor or workers for this service. Call 28-SNAKE to arrange for a site visit and worker training. It’s the right thing to do, its safety for your workers, and it’s the law!
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