Brown Tree Snake Colonization and Dispersal Events on Guam

1944: On June 15, Allied Forces begin the invasion of Saipan. Within two months, the Marianas are under control with primary importance as a base of operations for further attacks on Japan. As this happens, U.S. military equipment and salvaged war material that had been in use at the military bases in the Admiralty Islands of northern Papua New Guinea are shipped to the permanent bases in Guam. This continues through the final months of the war and for several years after World War II ends. The first stowaway snakes arrive to war-torn sites on Guam that undoubtedly were prime habitat for rats, introduced geckos, and other opportunistic species that rapidly invaded the recovering habitats.

1953: First written evidence of brown Treesnakes in the Apra Harbor area, which is most likely the introduction site on Guam. In this article, the sightings of snakes are still referred to as rumor. The article also says that if the snakes do exist "they are merely strays brought in from the outside," since snakes are not native to Guam save Ramphotyphlops braminus, a small worm snake that lives on the sandy beaches. Snakes sighted previously were not identified.

1955: Reports of snakes continue streaming in, and at least eight snakes have been documented and captured in the Apra Harbor area by this time. All are identified as Boiga irregularis, the brown Treesnake.

Mid 1960s: Snakes are reported throughout the southern and central parts of the island by civilians and members of the military.

1968: Snakes have spread throughout the island and are confirmed at the northernmost area of the island, Ritidian Point.

1970s-1980s: The snake population continues to grow exponentially with reports coming in from across the island, and declining bird populations are noticed.

Top of Page

Brown Treesnake Dispersal Events from Guam

Below are primarily confirmed reports of brown Treesnake activity outside of its native range and dispersing from Guam. When these reports are combined with a number of unconfirmed reports of brown tree snakes found in other areas, the only continents for which no reported arrivals exist are Antarctica and Africa.

Dispersal Events to Cocos

1988: Cocos Island is a day resort for tourists that lies just 3 km off the coast of Guam. The first brown Treesnake is discovered here in July. Since this small island is a refuge for remaining populations of lizards native to Guam and seabirds that previously nested on Guam, the entrance of the snake in this location is significant.

1989: In July, a second brown Treesnake makes its way to Cocos.

Dispersal Event to Corpus Christi, Texas

1993: On May 12, a brown tree snake makes its way to mainland U.S. for the first time. This snake is discovered in a crate of household goods en route from Guam. Delivered to Ingleside Naval Station on the north side of Corpus Christi Bay in Texas, the live snake, having endured 7 months in the crate since leaving Guam, falls out of the wrappings. It is quickly decapitated with a prybar.

Dispersal Event to Diego Garcia

1986: In June, a brown tree snake is discovered on a ship carrying naval cargo as it came to anchor off the island of Diego Garcia. Because this is a major military base in the Indian Ocean, there is strong probability that this snake was a stowaway from a stopover in Guam.

Dispersal Event to Kwajalein

1979: Only the second documented snake to leave Guam, a brown Treesnake is discovered on Kwajalein, Marshall Islands in April. The snake crawled out of the landing gear of a military cargo plane at what is now the Kwajalein Atoll Army installation.

Dispersal Events to Oahu, Hawaii

1981: In April, a juvenile brown Treesnake is found in the Customs area of the Honolulu Airport, having hitched its way presumably from Guam. In July, a second snake is discovered near an aircraft hangar at Barbers Point Naval Air Station.

1986: On May 5, a brown tree snake is found on Hickam Air Force Base after an early morning arrival from Guam.

1989: In October, yet another brown Treesnake makes its way to Hickam Air Force Base.

1991: The sporadic stream of snakes to Hawaii continues. On September 3, a brown Treesnake is found stunned near the tire of a parked plane on the Hickam Air Force Base runway. Just 8 hours later, another snake is found dead on the taxiway.

1994: In December, a brown Treesnake is again found on Oahu. The live subadult is discovered in an Army warehouse containing supplies recently shipped from Guam. Ironically, this snake was transported by truck from Hickam Air Force Base after its flight from Guam.

1997: In July, two military policemen report a brown snake on the alert pad of the Hawaii National Guard at Hickam Air Force Base, within 200 yards of the site where aircraft arriving from Guam are positioned upon landing. The snake eluded capture and was not confirmed as a brown Treesnake, but the circumstances warrant consideration as a possible dispersal event. The snake was never captured.

1998: In August, a brown tree snake is found dead in the wheelwell of a Continental Air Micronesia Airliner on Oahu, following two round-trip flights to Guam in the prior days.

Dispersal Event to Okinawa

1990: In July, a brown tree snake finds its way to a large American Air Force base on Okinawa, Ryukyu Islands, via military air traffic. Additional reports of brown Treesnakes at military bases on Okinawa are likely to have occurred but are not documented.

Dispersal Event to Pohnpei

1994: Serving as a wake-up call to the small Micronesian island, a brown Treesnake is found in a civilian cargo container that arrived from Guam.

Dispersal Events to Saipan

1986: Two brown Treesnakes are discovered on Saipan, one in June and the other in July.

1987: In July, another brown Treesnake is found.

1990: Two sightings are reported again this year, one in May and the other in November.

1991: Sightings are on the rise as four snakes are reported, one in March, two in April, and one in December.

1992: The risk of settlement by the brown Treesnake on Saipan becomes more credible as seven sightings are made, two in March, one in April, two in May, and two in September.

Dispersal Event to Rota

1991: In a relatively short passage by a brown Treesnake, one is discovered on nearby Rota in October. Just 47 miles northeast of mainland Guam, sites on Rota have been used for releasing the Guam rail, which was extirpated on Guam by the brown Treesnake and has since been captively bred in zoos. The sites on Rota were particularly attractive for establishment of rails because the ecosystem is similar to what existed on Guam before the introduction of the brown Treesnake.

Dispersal Events to Tinian

1990: The first discovery of a brown Treesnake on Tinian occurs in February, providing an indication of the possible risk for this small Micronesian island regarding the snake. Tinian holds a number of rare and/or endemic species without snake predators as did Guam before its snake irruption.

1994: The alarm is reinforced as a sudden flood of brown Treesnakes reaches Tinian. Four snakes were reported in November in association with appliances shipped from Guam.

Dispersal Event to Wake Island

1949: Although the snakes have not yet reached maximum densities on Guam, they are already reaching other destinations from or through Guam. In February, a brown Treesnake is discovered near a naval facility on Wake Island, having found its way into cargo materials in a ship returning from the South Pacific through Guam.

Positive identification is made by a naval employee with experience in Guam.

Top of Page

Important Continental Dispersal Events

Singapore, Southeast Asia

An unconfirmed incident forwarded to the United States Geological Survey (USGS) from military personnel on Guam reported a brown Treesnake found on a Navy jet after the plane had arrived at a military base on Singapore from Guam. The plane reportedly had been on Guam only for a few hours for fuel and a possible crew change. The presence of a snake after such a short stop in Guam highlights the potential risks to even transiting aircraft and cargo.

Mainland Japan

During casual conversation with a pilot from Northwest Airlines, a USGS researcher was told of brown Treesnakes being discovered on commercial airliners landing at major Japanese airports. Although no details were provided and this dispersal route has not been confirmed, the large number of commercial flights daily between Guam and Japan by Northwest, Continental/Air Micronesia, and Japan Airlines is concordant with the risk of dispersal to major Japanese cities.

Taiwan

The discovery of a large brown Treesnake on a DC-10 aircraft while in Taiwan for major renovation of cabin configuration and seating has been mentioned by several residents of Micronesia and the Marianas, with the information being attributed to an employee of Continental Air Micronesia. The snake supposedly was found hidden behind cosmetic ceiling panels removed during the modernization of the plane's interior.

Darwin, Northern Territory, Australia

A large brown Treesnake with a color pattern resembling that found on snakes on Guam was discovered on a U.S. Air Force B-52 bomber in 1984 after it landed near Darwin, Northern Territory, from Guam. According to Dr. Paul Horner, the Australian herpetologist who provided the information, the snake was recognized as a stowaway on the basis of its coloration — which is quite different from the beige with red saddles color pattern typical of this species in the Northern Territory of Australia.

Rota, Spain

The discovery of a brown Treesnake in May 1994 in a military household goods shipment arriving to Rota, Spain, was reported by a man who was formerly the manager of the Navy Golf Course on Guam. Hence, the observer had some familiarity with the brown Treesnake on Guam. The snake was reportedly found alive in the shipment, even though it had been in transit and storage in Pensacola, Florida, for several months. This case is particularly interesting because it could have served as a possible introduction to Europe and the Mediterranean Region for the brown Treesnake had it not been discovered. However, the snake's identification was not confirmed by an expert.


	Home Jobs About
FORT > Resources > Education > BTS Home Page > Invasion of a Predator > BTS Colonization Brown Treesnake Colonization and Dispersal Events on Guam Timeline of the Brown Treesnake's Travel Across Guam Brown Treesnake Dispersal Events from Guam Important Continental Dispersal Events Timeline of the Brown Treesnake's Travel Across Guam 1944: On June 15, Allied Forces begin the invasion of Saipan. Within two months, the Marianas are under control with primary importance as a base of operations for further attacks on Japan. As this happens, U.S. military equipment and salvaged war material that had been in use at the military bases in the Admiralty Islands of northern Papua New Guinea are shipped to the permanent bases in Guam. This continues through the final months of the war and for several years after World War II ends. The first stowaway snakes arrive to war-torn sites on Guam that undoubtedly were prime habitat for rats, introduced geckos, and other opportunistic species that rapidly invaded the recovering habitats. 1953: First written evidence of brown Treesnakes in the Apra Harbor area, which is most likely the introduction site on Guam. In this article, the sightings of snakes are still referred to as rumor. The article also says that if the snakes do exist "they are merely strays brought in from the outside," since snakes are not native to Guam save Ramphotyphlops braminus, a small worm snake that lives on the sandy beaches. Snakes sighted previously were not identified. 1955: Reports of snakes continue streaming in, and at least eight snakes have been documented and captured in the Apra Harbor area by this time. All are identified as Boiga irregularis, the brown Treesnake. Mid 1960s: Snakes are reported throughout the southern and central parts of the island by civilians and members of the military. 1968: Snakes have spread throughout the island and are confirmed at the northernmost area of the island, Ritidian Point. 1970s-1980s: The snake population continues to grow exponentially with reports coming in from across the island, and declining bird populations are noticed. Top of Page Brown Treesnake Dispersal Events from Guam Below are primarily confirmed reports of brown Treesnake activity outside of its native range and dispersing from Guam. When these reports are combined with a number of unconfirmed reports of brown tree snakes found in other areas, the only continents for which no reported arrivals exist are Antarctica and Africa. Dispersal Events to Cocos 1988: Cocos Island is a day resort for tourists that lies just 3 km off the coast of Guam. The first brown Treesnake is discovered here in July. Since this small island is a refuge for remaining populations of lizards native to Guam and seabirds that previously nested on Guam, the entrance of the snake in this location is significant. 1989: In July, a second brown Treesnake makes its way to Cocos. Dispersal Event to Corpus Christi, Texas 1993: On May 12, a brown tree snake makes its way to mainland U.S. for the first time. This snake is discovered in a crate of household goods en route from Guam. Delivered to Ingleside Naval Station on the north side of Corpus Christi Bay in Texas, the live snake, having endured 7 months in the crate since leaving Guam, falls out of the wrappings. It is quickly decapitated with a prybar. Dispersal Event to Diego Garcia 1986: In June, a brown tree snake is discovered on a ship carrying naval cargo as it came to anchor off the island of Diego Garcia. Because this is a major military base in the Indian Ocean, there is strong probability that this snake was a stowaway from a stopover in Guam. Dispersal Event to Kwajalein 1979: Only the second documented snake to leave Guam, a brown Treesnake is discovered on Kwajalein, Marshall Islands in April. The snake crawled out of the landing gear of a military cargo plane at what is now the Kwajalein Atoll Army installation. Dispersal Events to Oahu, Hawaii 1981: In April, a juvenile brown Treesnake is found in the Customs area of the Honolulu Airport, having hitched its way presumably from Guam. In July, a second snake is discovered near an aircraft hangar at Barbers Point Naval Air Station. 1986: On May 5, a brown tree snake is found on Hickam Air Force Base after an early morning arrival from Guam. 1989: In October, yet another brown Treesnake makes its way to Hickam Air Force Base. 1991: The sporadic stream of snakes to Hawaii continues. On September 3, a brown Treesnake is found stunned near the tire of a parked plane on the Hickam Air Force Base runway. Just 8 hours later, another snake is found dead on the taxiway. 1994: In December, a brown Treesnake is again found on Oahu. The live subadult is discovered in an Army warehouse containing supplies recently shipped from Guam. Ironically, this snake was transported by truck from Hickam Air Force Base after its flight from Guam. 1997: In July, two military policemen report a brown snake on the alert pad of the Hawaii National Guard at Hickam Air Force Base, within 200 yards of the site where aircraft arriving from Guam are positioned upon landing. The snake eluded capture and was not confirmed as a brown Treesnake, but the circumstances warrant consideration as a possible dispersal event. The snake was never captured. 1998: In August, a brown tree snake is found dead in the wheelwell of a Continental Air Micronesia Airliner on Oahu, following two round-trip flights to Guam in the prior days. Dispersal Event to Okinawa 1990: In July, a brown tree snake finds its way to a large American Air Force base on Okinawa, Ryukyu Islands, via military air traffic. Additional reports of brown Treesnakes at military bases on Okinawa are likely to have occurred but are not documented. Dispersal Event to Pohnpei 1994: Serving as a wake-up call to the small Micronesian island, a brown Treesnake is found in a civilian cargo container that arrived from Guam. Dispersal Events to Saipan 1986: Two brown Treesnakes are discovered on Saipan, one in June and the other in July. 1987: In July, another brown Treesnake is found. 1990: Two sightings are reported again this year, one in May and the other in November. 1991: Sightings are on the rise as four snakes are reported, one in March, two in April, and one in December. 1992: The risk of settlement by the brown Treesnake on Saipan becomes more credible as seven sightings are made, two in March, one in April, two in May, and two in September. Dispersal Event to Rota 1991: In a relatively short passage by a brown Treesnake, one is discovered on nearby Rota in October. Just 47 miles northeast of mainland Guam, sites on Rota have been used for releasing the Guam rail, which was extirpated on Guam by the brown Treesnake and has since been captively bred in zoos. The sites on Rota were particularly attractive for establishment of rails because the ecosystem is similar to what existed on Guam before the introduction of the brown Treesnake. Dispersal Events to Tinian 1990: The first discovery of a brown Treesnake on Tinian occurs in February, providing an indication of the possible risk for this small Micronesian island regarding the snake. Tinian holds a number of rare and/or endemic species without snake predators as did Guam before its snake irruption. 1994: The alarm is reinforced as a sudden flood of brown Treesnakes reaches Tinian. Four snakes were reported in November in association with appliances shipped from Guam. Dispersal Event to Wake Island 1949: Although the snakes have not yet reached maximum densities on Guam, they are already reaching other destinations from or through Guam. In February, a brown Treesnake is discovered near a naval facility on Wake Island, having found its way into cargo materials in a ship returning from the South Pacific through Guam. Positive identification is made by a naval employee with experience in Guam. Top of Page Important Continental Dispersal Events Singapore, Southeast Asia An unconfirmed incident forwarded to the United States Geological Survey (USGS) from military personnel on Guam reported a brown Treesnake found on a Navy jet after the plane had arrived at a military base on Singapore from Guam. The plane reportedly had been on Guam only for a few hours for fuel and a possible crew change. The presence of a snake after such a short stop in Guam highlights the potential risks to even transiting aircraft and cargo. Mainland Japan During casual conversation with a pilot from Northwest Airlines, a USGS researcher was told of brown Treesnakes being discovered on commercial airliners landing at major Japanese airports. Although no details were provided and this dispersal route has not been confirmed, the large number of commercial flights daily between Guam and Japan by Northwest, Continental/Air Micronesia, and Japan Airlines is concordant with the risk of dispersal to major Japanese cities. Taiwan The discovery of a large brown Treesnake on a DC-10 aircraft while in Taiwan for major renovation of cabin configuration and seating has been mentioned by several residents of Micronesia and the Marianas, with the information being attributed to an employee of Continental Air Micronesia. The snake supposedly was found hidden behind cosmetic ceiling panels removed during the modernization of the plane's interior. Darwin, Northern Territory, Australia A large brown Treesnake with a color pattern resembling that found on snakes on Guam was discovered on a U.S. Air Force B-52 bomber in 1984 after it landed near Darwin, Northern Territory, from Guam. According to Dr. Paul Horner, the Australian herpetologist who provided the information, the snake was recognized as a stowaway on the basis of its coloration — which is quite different from the beige with red saddles color pattern typical of this species in the Northern Territory of Australia. Rota, Spain The discovery of a brown Treesnake in May 1994 in a military household goods shipment arriving to Rota, Spain, was reported by a man who was formerly the manager of the Navy Golf Course on Guam. Hence, the observer had some familiarity with the brown Treesnake on Guam. The snake was reportedly found alive in the shipment, even though it had been in transit and storage in Pensacola, Florida, for several months. This case is particularly interesting because it could have served as a possible introduction to Europe and the Mediterranean Region for the brown Treesnake had it not been discovered. However, the snake's identification was not confirmed by an expert. Top of Page	The BTS on Guam (Home) Biology of the BTS & Pacific Snakes Invasion of a Predator Impacts & Damages from the BTS Control & Containment of the BTS Frequently Asked Questions Related Resources Report Snake Sightings! Table of Contents Search FORT
Staff Directory \| Science Branches \| Product Library \| News & Events \| Science Features
U.S. Department of the Interior U.S. Geological Survey 2150 Centre Avenue, Bldg C Fort Collins, CO 80526-8118 URL: http://www.fort.usgs.gov/ Last Modified: 26.07.2005 10:21 Web Coordinator: Lance Everette
FORT Questions and Comments \| Privacy \| Disclaimer \| Freedom of Information Act \| Accessibility

Brown Treesnake Colonization and Dispersal Events on Guam

Timeline of the Brown Treesnake's Travel Across Guam

Brown Treesnake Dispersal Events from Guam

Important Continental Dispersal Events

Timeline of the Brown Treesnake's Travel Across Guam

Top of Page

Brown Treesnake Dispersal Events from Guam

Dispersal Events to Cocos

Dispersal Event to Corpus Christi, Texas

Dispersal Event to Diego Garcia

Dispersal Event to Kwajalein

Dispersal Events to Oahu, Hawaii

Dispersal Event to Okinawa

Dispersal Event to Pohnpei

Dispersal Events to Saipan

Dispersal Event to Rota

Dispersal Events to Tinian

Dispersal Event to Wake Island

Top of Page

Important Continental Dispersal Events

Singapore, Southeast Asia

Mainland Japan

Taiwan

Darwin, Northern Territory, Australia

Rota, Spain

Report Snake Sightings!