The Brown Tree Snake (Boiga irregularis) is an invasive species on the island of Guam that is wreaking a lot of havoc. This snake was introduced onto the island of Guam after WWII. People speculate that is was brought here by a military transport from Solomon Islands (Environment p23). People also say that it could have stowed away on a military aircraft. There are even people who say that the snake was introduced by the US Government to help control the rat problem (Audubon p26). However they got to Guam, the fact is that the snakes are there and causing massive environmental damage.
The brown tree snake grows to a length of around eight feet (National Wildlife p15). There have been some reports of snakes up to ten feet long (Smithsonian p113). It has budging yellow eyes with a black slit for an iris in them. It has a large head compared to its slender body (National Wildlife p16). This snake is a constrictor squeezing the life out of its prey. It also is a venomous snake the produces the poison in the back of its mouth paralyzing its prey while it crushes them to death. Although it is a poisonous snake the venom is relatively harmless to humans since it is produced in the back of the mouth and the snake has no way of quickly injecting it into a person (US News and World Reports p13)
This snake is a problem to the bird population. For millions of years these birds have been isolated to Guam. For this entire time these birds have also had no natural predators until now. This snake is an extraordinary climber. Its slender body enables it to maneuver around the tops of the branches where most of the birds roost (National Wildlife p16). This snake has wiped out 9 out of the 12 native species in Guam. The rufus fronted fantail, the Guam broad-bill, and the bridled white-eye are now extinct (National Wildlife p15). Many of the other birds such as the Guam rail and the Guam Micronesian kingfisher shortly existed only in captivity, the brown tree snake wiping out all of the native population. The forests that once echoed with birdcalls are now silent.
How was this snake discovered to be the problem behind the sudden disappearance of the bird population on Guam? Many people believed that the sudden drop was cause by a virus or maybe mongooses had been introduce. Julie Savidge, a graduate student from the University of Illinois, came to the island in 1981 and began to search for clues for the reason why the sudden demise of the bird population. She says, "I fully expected to identify some sort of exotic disease." She collected live and dead bird and could find no reason for their extinction. The natives were telling her that she was wasting her time because they said the cause was the brown tree snake. Julie began to examine the snake closely. It turns out that the spread of the snake population across the island matched perfectly to the decline of the birds of the island. She also found a dramatic drop in the population of small mammals such a mice, shrews, and rats. She began to set traps with quail in them in order to catch the murderer red handed. Seventy-five percent of the quail were eaten within the first four nights at places where the native birds were gone and snakes had taken hold (National Wild life p 14).
People began to wonder if the bird population was crashing why wasn't the snake population crashing as well. In some areas the snake had a population of twelve thousand to thirty thousand snakes per square mile (National Wildlife p16 and Smithsonian p118). Surely with this high of a snake density they would have passed the threshold of how many snakes an ecosystem can support. By passing the threshold the snake population should logically crash as well. The answer was that the snakes were feeding on other introduced species. They were feeding on non-native birds, lizards, and skinks. The relationship between the skinks and the snakes is an interesting one. Both are introduced species. The young snakes feed off of the high number of skinks allowing more snakes to survive into adult hood. Fred Kraus, the alien species coordinator for Hawaii Department of Land and Natural Resources says, "The relationship between skinks and the brown tree snake's population is an example of what happens when you introduce nonnative plants and animals into a place. You can get a synergistic effect, things you never expected." (National Wildlife p17)
These snakes are not only a problem for the local bird population; they are also a problem for the people living on the island as well. People have given up raising chickens and pigeons because the snakes were wreaking havoc on their flocks (Smithsonian p113). Snakes cause an estimated power outage on the island once every three days (National Wildlife p16). These power outages are cause when the snakes slither into transformers causing the power outages while electrocuting themselves to death in the process. These power outages affect everyone on the island including the US military base on the island. These snakes have also been known to attack small children while they sleep. Guam's public heath records indicate that 74 toddlers were treated for snakebites between 1985 and 1995 (National Wildlife p16.)
Where will these veracious predators travel next? People are suspecting that they will likely target Hawaii next. Tom Fritts, a research biologist with the US Geological Survey says, "Its only a matter of time." (Newsweek p13) These reptiles could get to Hawaii the same way that they came to Guam. They could hitch hike on a transport of some kind such as a plane or ship coming to Hawaii. Measures are being taken to try and help protect Hawaii from such devastations. Since Hawaii has no native snakes on the island, they take snakes very seriously. The state imposes a fine as high as $25,000 for importing or owning a snake of any type. On Hawaii there are snake-sniffing dogs. Hawaii has five beagles sniffing out snakes that arrive on both commercial and military flights from Guam. Because of short funding for this program though not all military flights are inspected (National Wildlife p17). Even letting one snake through can cause massive devastation for Hawaii. Like most snakes, the female brown tree snake is able to store sperm to fertilize her eggs for several years after mating (Audubon p26). So in theory, if the right snake slips through then the snakes could gain a solid foothold in Hawaii and begin its devastation there. There are signs that the snakes are beginning to slip through the border patrols. In 1981 two snakes were found and destroyed in Oahu, two more were found in 1986. In 1991 two snakes were found on in the same day at unrelated sights. One was found on the taxiway at Honolulu Airport and the other under a military cargo plane at the adjacent Hickam Air Force Base. All the snakes that were found were destroyed (Audubon p26). These snakes that were destroyed were just the ones that were caught. It is possible that snakes have slithered off into the wilderness. In fact there have been many unconfirmed sighting of the snake on the island of Hawaii. These sightings may have been the brown tree snake or they could have been pythons and boas that were former pets released into the wild which is also illegal.
The national government is taking the invasion of the snake seriously as well. In December of 1991 President George Bush signed into law the Brown Tree Snake Control Act of 1991 (Audubon p26). This act directs the Secretary of Agriculture to "institute a program of suppression, control, eradication, and research. On February 3, 1999 President Bill Clinton signed an executive order creating new federal interagency Invasive Species Council. This council has 18 months to produce a broad management plan to limit the effects of invasive species. In addition an advisory committee of stakeholders is to provide expert input to the council. The President has also ordered all agencies to ensure that their activities are maximally effective against invasive species. To continue on his action against invasive species the presidents FY 2000 budget includes and additional $29 million for projects to fight invasive species and restore ecosystems damaged by them (Issues in Science and Technology p25). In response to this new funding the US Department Of Agriculture has is working on new ways to deal with the snakes. Larry Clark of the USDA has developed a spray the severely irritates the snake. This spray in the future could be used to flush snakes out of their hiding places to make it easier for the dogs to find them. Peter Savarie also from the USAD is conducting research to find out what kind of tube the snake would most like to hide in. The idea would be to paint the inside of the tubes with poison for the snakes to slither through thus helping to eliminate the problem of snakes hitching rides on cargo. Other scientists are also experimenting with a flu virus to exterminate the snakes (US News and World Reports p13). This idea is similar to the way the Australians are dealing with the rabbits that have over populated their continent. These rabbits are also an invasive species. Unfortunately the virus ended up killing many domesticated rabbits and some say the virus could be passed on to humans (Newsweek p13).
Overall the brown tree snake has cause horrendous damage to the Island of Guam. Louisiana State Ornithologist Douglass Pratt calls the snake and what it has done to Guam, "The greatest avian disaster of the twentieth century." (National Wildlife p13) This snake has pushed nine out of twelve native birds to the brink of extinction while actually crossing the point of no return with three of the species. Many things are being done to stop the spread of this species to other islands where is could cause as much, if not more ecological damage. Guam itself has 14 snake sniffing Jack Russell Terriers and 1400 snake traps around airports and other targeted sights. These measures catch 3,000 to 5,000 snakes per year but with almost double that number per square mile it is little wonder that it not making that big of a dent in the snake population. There is one way to control this invasive species but not many of the natives are open to the idea. The brown tree snakes natural predator in the King Cobra (US News and World Reports p13). If this were to be introduced as well then there would be a food chain of invasive species starting with the skinks eaten by the brown tree snake then in turn eaten by the King Cobra. This solution would not happen though because people do no want this highly venomous and dangerous snake introduced on to Guam. After all who knows what effects it would have other native species? One thing is for sure though. Many measures have been taken and some of the bird populations may rebound but it is unlikely that Guam will ever be free of the brown tree snake or that it will ever return to its former glory.
Audubon "Strangers In Paradise" v94 n3 May 1992 p24-26
Environment "Tree Snake Tourists in Hawaii" v36n3 June 1993 p23
Issues in Sciences and Technology "As Invasive Species Threat Intensifies, US Steps Up Fight" v15 n3 Spring 1999 p25
National Wildlife "Massacre on Guam" John Carey, v26 n5 August 1988 p12-15
National Wildlife "A State Without Snakes Keeps A Wary Eye Out For An Alien Invader" Ann Rillero, v36 n4 June/July 1988 p16-17
Newsweek "Invasion of the Tree Snakes and Other Coming Infestations" v130 n4 p13
Smithsonian "The Rail and the Rail: A War In the Pacific" S. Dillon Ripley, v22 n5 Aug 1991 p112-119
US News and World Reports "The Uninvited Guest" v122 n21 June 12 1997 p13
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