Management Information
In 1995 the brown tree snake (Boiga irregularis) was listed by the US Department of Agriculture as among the top three pests requiring control and eradication (Source: SPREP). No large-scale eradication programmes have been employed, however, traps, visual inspections, trained dogs and specialised barriers are in use. Toxicants and bio-control are in development. Efforts are being made to develop artificial attractants. Snake barriers have been used in some situations; vinyl barriers are durable, but the surface finish may degrade over time. Surfaces must be smooth to deter the snake from attempting to climb the barrier. Masonry barriers use a pre-stressed moulded concrete design which is 100% successful in keeping snakes out and is not vulnerable to rat or typhoon damage. However, it has a high initial cost of approximately US$300 per metre. There are currently approximately 2500 snake traps on Guam (Rodda et al. 2002).
Guam's importance as a trans-Pacific shipping hub, coupled with the tendency of snakes to seek refuge in cargo make snake dispersal from Guam a serious threat to other island ecosystems (Fritts 1988; Fritts et al. 1999; Vice et al 2003; Vice Engeman and Vice 2005). Because of this, the major mission of Commander Naval Forces Marianna Naval Base, Guam is to ensure the brown tree snake does not move to other islands. If it moves to Hawaii or the mainland it is considered to reek havoc (Westbrook and Ramos 2005). Brown tree snakes can easily hide in ships moving between islands and are currently being moved to new islands in aircraft cargo. Several tree snakes have been detected at Honolulu airport in recent years. Preventing their spread depends on the maintenance of continuous checking of ships and aircraft cargo. Detector dogs are in use in the Northern Mariana Islands (Perry 1998). The Global Invasive Species Programme (GISP) is fostering a cooperative effort among experts in Guam, Australia, Hawaii and mainland USA in an effort to combat this pest.
A variety of snake traps have been used on Guam; most consisting of a modified crawfish or minnow trap, housing a live mouse that serves as a lure (Vice Engeman and Vice 2005). The traps are hung on vegetation or along security fences (Vice Engeman and Vice 2005). New techniques are also being developed, such as "pinkies with parachutes", which consist of deceased newborn mice filled with acetametaphine and fitted with tiny parachutes that allow them to drift into trees. As the brown tree snake is arboreal it is more likely to come across the mouse if it is in the tree and, because it has a parachute, the bait may land in positions that would be inaccessible to humans setting traps from the ground (Westbrook and Ramos 2005).
Location Specific Management InformationArea 50 (Guam)
Snake control was initiated in Area 50 prior to the construction of a snake-proof bulge barrier in 1997. This reduced the snake population, but has not eradicated it. Snakes continue to be caught at persistent capture rates, between zero to seven snakes a week.Area 50 is a 23 ha patch of forest on Anderson Air Force Base. It contains a released population of the endangered Guam rail (Gallirallus owstoni see IUCN Red List of Threatened Species). Guam
There are no large-scale eradication methods currently available. Traps, visual inspections, trained dogs and specialized barriers are in use; and toxicants and bio-control methods are in development. Given the difficulty in eradicating B. irregularis once it is established, it is crucial to prevent its further spread in the Pacific region by maintaining very strict cargo checks of boats and searches at airports at all times. Small predator-free nature reserves can be created using a combination of snake barrier and eradication techniques. Campbell (1996) eliminated brown tree snakes from two 1 ha reserves, using barriers. Lizard numbers increased rapidly in the enclosed area. The barrier had two main problems, that of rats which chewed holes in the barrier, and typhoons which caused damage to the barrier. Further research has identified four possible designs for a successful barrier. Temporary barriers used for interdicting snakes in commerce, are unsuitable for reserves. Bulge barriers are used as a low-cost option, but are vulnerable to typhoons and therefore not permanent. Vinyl barriers are durable, but the surface finish may degrade over time. If the surface does not remain smooth, the snake may climb the barrier. Masonry barriers use a pre-stressed moulded concrete design which is 100% successful in keeping snakes out and is not vulnerable to rat or typhoon damage. However, it has a high initial cost of approximately US $ 300 /m. Currently, Wildlife Services maintain 2000-3000 snake traps on Guam (Rodda et al. 2002). Saipan Is. (Northern Mariana Islands)
The eradication of brown tree snakes from Saipan may be hindered by the abundance of prey on the island.
Management Resources/Links
3. Fritts, T. H. 1987. Movements of snakes via cargo in the Pacific region. 'Elepaio 47: 17-18. 4. Fritts, T. H. 1988. The brown tree snake, Boiga irregularis, a threat to Pacific Islands. U.S. Fish and Wildlife Service Biological Reports 88(31). 36pp. 5. Gee II, David E., pers. comm. 2006. Wildlife Biologist, Guam Division of Aquatic & Wildlife Resources and Guam team member of the Pacific Invasives Learning Network (PILN). 7. Rodda & Savage, 2007. Impact of Invasive Boiga irregularis, the Brown Tree Snake. Pacific Science
Summary: Contains information about impacts of the brown tree snake including costs in terms of economy as as well as ecologically. Also contains description of the species as well as management information. 8. Rodda, G. H., Sawai, Y., Chiszar, D. and Tanaka, H. (eds) 1999. Problem snake management: the Habu and the Brown Treesnake. Cornell Univ. Press, Ithaca, New York: 534pp.
Summary: This book summarizes the state of knowledge as of 1999 - a nice and broad compilation that lists just about everything else of use to that date. 10. USDA National Agricultural Library., 2008. Species profiles: Brown Tree snake
Summary: The U.S.Geological Survey has assumed a central role in studying the biology of the brown tree snake, the problems it can cause and alternatives for control. USGS researchers are also examining how ecological health is jeopardized on Guam and other islands.
Available from: http://www.invasivespeciesinfo.gov/animals/bts.shtml [Accessed 21 February 2008] 11. Vice, D.S., Engeman, R.M. and Vice, D.L. 2005. A Comparison of Three Trap Designs for Capturing Brown Treesnakes on Guam, Wildlife Research 32: 355-359. 12. Westbrook, C. and Ramos, K. 2005. Under Siege: Invasive Species on Military Bases. National Wildlife Federation. 13. Wiles, G. J., Bart, J., Beck Jr. R. E., and Aguan, C.F., 2003. Impacts of the Brown Tree Snake: Patterns of Decline
and Species Persistence in Guam’s Avifauna. Conservation Biology, Volume 17, No. 5.
Summary: Impacts of brown tree snake on endemic species in Guam. Results Page: 1
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