Overview

Brief Summary

Boiga irregularis is a nocturnal, oviparous, and arboreal snake in the family Colubridae. It is widely regarded as an invasive species, especially after decimating Guam’s native bird and lizard populations. It is a generalist predator with few to no predators of its own; both features have enabled its population explosion in Guam.

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Distribution

Boiga irregularis is native to the northern and eastern coasts of Australia, the Soloman Islands, and Papua New Guinea (Rodda et al. 1999). It was introduced to Guam after World War II, where it successfully estabilished a population, taking over previously unoccupied niches and decimating native species (Rodda et al. 1992). Consequentially, Boiga irregularis is one of the 100 worst invasive species worldwide (Lowe et al. 2000).

References

Lowe, S., M. Browne, S. Boudjelas, and M. De Poorter. 2001. 100 of the world's worst invasive alien species: a selection from the global invasive species database. Species Survival Commission, World Conservation Union, Auckland, New Zealand.

Rodda, G. H., T. H. Fritts, and P. J. Conry. 1992. Origin and population growth of the Brown tree snake, Boiga irregularis, on Guam. Pacific Science 46: 46–57.

Rodda, G. H., T. H. Fritts, M. J. McCoid, and E. W. Campbell. 1999. An overview of the biology of the brown treesnake (Boiga irregularis), a costly introduced pest on Pacific islands. Problem snake management: the habu and the brown treesnake. Cornell University Press, Ithaca, New York. pp. 44-80.

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Continent: Oceania Asia Australia
Distribution: Indonesia (Sulawesi: Togian Islands), New Guinea, Australia (New South Wales, North Territory, Queensland, West Australia), Guam (introduced), Solomon Islands [McCoy 2000], Caroline Islands (Pohnpei)  
Type locality: unknown
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Source: The Reptile Database

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Physical Description

Morphology

Boiga irregularis is a nocturnal, arboreal colubrid and its morphology is representative of this fact. Boiga irregularis has a slender body that allows it to easily bridge gaps in vegetation. It also has low mass relative to its length, which allows it to minimize its mass while distributing it over many support points. It has a prehensile tail, which it uses to grip branches and anchor itself when being shaken or pulled from trees. Its head is larger than the neck and has extremely elastic soft tissues which let it consume larger prey (Rodda et al. 1999). Correlated with its nocturnal habit, Boiga irregularis has laterally directed eyes with elliptical pupils (Lillywhite and Henderson 1993). Unlike most other nocturnal snakes, it lacks a reflective layer in the retina and so has no eye shine.

Boiga irregularis has a variety of color morphs, though coloration is usually constant within localities (Rodda et al. 1992). In Australia, markings range from dark blotches on a background of brown to yellow, to blue and white or red and white banding (Cogger 1992).

Boiga irregularis has venom glands and rear fangs, but these are believed to be due to its phylogenetic history, a characteristic of the Colubridae family, rather than its ecology (Rodda et al. 1999). When its venom glands were removed, B. irregularis were still able to quickly subdue and kill prey by constriction, proving it did not depend on venom for predation (Rochelle and Kardong 1993). In the wild, a combination of constriction and venom may help in predation against larger, more resistant prey (Mackessy et al. 2006).

Size

Total length is the only obvious sexual dimorphism of Boiga irregularis. In Guam, females grow to 2.3 m and males grow to 3.1 m. The smallest snakes found in the wild were 330-350 mm snout-vent length (SVL; Rodda et al. 1999). In New Guinea, B. irregularis reach lengths of at least 2.3 m (Parker 1982).

References

Cogger, H. G. 1992. Reptiles and Amphibians of Australia, 5th ed. Ithaca: Cornell Univ. Press.

Lillywhite, H. B., and Henderson, R. W. 1993. Behavioral and functional ecology of arboreal snakes. Snakes: Ecology and Behavior. New York: McGraw-Hill. pp. 1-48.

Mackessy, S. P., Sixberry, N. M., Heyborne, W. H., and Fritts, T. 2006. Venom of the brown treesnake, Boiga irregularis: ontogenetic shifts and taxa-specific toxicity. Toxicon 47: 537.

Parker, F. The Snakes of the Western Province: Wildlife in Papua New Guinea. Division of Wildlife, Department of Lands & Environment, 1982.

Rochelle, M. J. and Kardong, K. V. 1993. Constriction vs. envenomation in prey capture by the Brown Treesnakes Boiga irregularis (Squamata: Colubridae). Herpetologica 49: 297–300.

Rodda, G.H. 1992. Foraging behaviour of the Brown Tree Snake, Boiga irregularis. Herpetological Journal 2: 110-114.

Rodda, G. H., T. H. Fritts, M. J. McCoid, and E. W. Campbell. 1999. An overview of the biology of the brown treesnake (Boiga irregularis), a costly introduced pest on Pacific islands. Problem snake management: the habu and the brown treesnake. Cornell University Press, Ithaca, New York. pp. 44-80.

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Ecology

Habitat

While radiotelemetry data shows Boiga irregularis often traveling through various types of both forested and non-forested areas, Boiga irregularis prefers densely foliated arboreal habitats (Rodda et al. 1999). Even so, they travel extensively on the ground, making use of grasslands and shrub lands (Santana-Bendix 1994). When traveling on the ground with little cover, Boiga irregularis seek safety by climbing any nearby structure (such as power poles, buildings, trees, etc.) when threatened (Rodda 1991).

In Guam, the highest sighting rates of Boiga irregularis occurred in tangantangan trees (Leucuenu leucocephala), but this may be due to the ease at which searchers could see through small, folded leaves characteristic of the trees (Rodda 1992).

References

Rodda, G.H. 1991. Fence climbing by the arboreal snake Boiga irregularis. Snake 23: 101-103.

Rodda, G. H., T. H. Fritts, M. J. McCoid, and E. W. Campbell. 1999. An overview of the biology of the brown treesnake (Boiga irregularis), a costly introduced pest on Pacific islands. Problem snake management: the habu and the brown treesnake. Cornell University Press, Ithaca, New York. pp. 44-80.

Santana-Bendix, M. 1994. Movements and activity patterns of the Brown Tree Snake (Boiga irregularis) on the island of Guam. Master’s Thesis, Univ. of Arizona.

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Trophic Strategy

Boiga irregularis are generalist predators and eat a variety of prey. Though it is an introduced species in Guam, their diet is very similar to those living in their native range. They feed on small mammals, lizards, and birds. While there are no differences between males and females in either the type and number of prey consumed, there are differences among size classes. Boiga irregularis in the smallest size class (< 120 cm SVL) predominately feed on lizards and lizard eggs, whereas those in the largest size class (> 150 cm SVL) feed on birds, bird eggs, and mammals. The medium size class (120-150 cm SVL) has the most inclusive diet, feeding on lizards and their eggs, birds and their eggs, and mammals (Savidge 1988).

References

Savidge, J. A. 1988. Food habits of Boiga irregularis, an introduced predator on Guam. Journal of Herpetology 22: 275-282.

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Associations

Predation on Boiga irregularis

There is one published account of predation of Boiga irregularis. In Australia, there were two reported instances of predation by red-bellied black snakes, Pseudechis porphyriacus, and one instance of predation by a cane toad, Bufo marinus (Caudell et al. 2000).

References

Caudell, J.N., B. James, and P. Lawie. 2000. Boiga irregularis (brown tree snake): predation. Herpetological Review 31: 245.

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Known prey organisms

Boiga irregularis preys on:
Suncus murinus

This list may not be complete but is based on published studies.
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Diseases and Parasites

In Guam, a small sample of Boiga irregularis were tested for internal parasites but none was found. In New Guinea, two snakes were tested for oral parasites (Rodda et al. 1999). One did not have any bacteria and the other had Escherichia coli (Ross and Marzec 1984). Neither demonstrated signs of being affected by disease.

References

Rodda, G. H., T. H. Fritts, M. J. McCoid, and E. W. Campbell. 1999. An overview of the biology of the brown treesnake (Boiga irregularis), a costly introduced pest on Pacific islands. Problem snake management: the habu and the brown treesnake. Cornell University Press, Ithaca, New York. pp. 44-80.

Ross, R. A., and G. Marzec. 1984. The Bacterial Diseases of Reptiles: Their Epidemiology, Control, Diagnosis and Treatment Stanford, Calif.: Institute for Herpetology Research.

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Life History and Behavior

Behavior

Activity

Boiga irregularis is nocturnal. This is evidenced by the increase in Guam power outages caused by Boiga irregularis at night (Fritts et al. 1987). These power outages peak at midnight and taper off as morning approaches. While most movement occurs at night, the snakes remain alert and responsive during the day (Chiszar et al. 1985).

Social Interactions

While snakes generally are not regarded as social creatures, there is evidence that Boiga irregularis tolerates the presence of other snakes when finding suitable refugia (Hoser, 1980). Aggregations of Boiga irregularis in trees and rock crevices in Guam demonstrate this tolerance, though no social structure or pattern is apparent; all sizes, sexes, and ages were present (Savidge 1986).

Defense

The first line of defense for Boiga irregularis is relying on crypsis, concealment, or staying motionless in response to a predator. It spends most of the day basking in the tree canopy, remaining motionless. If approached by an aerial predator, it will drop out of the tree to avoid capture. Boiga irregularis only uses aggressive defense mechanisms, such as coiling and/or striking out, as a last resort if cornered or captured (Rodda et al. 1999).

References

Chiszar, D., D. Carrillo, P. Rand, J. Chiszar, and H. M. Smith. 1985. Nocturnal activity in captive Brown Tree Snakes Boiga irregularis. Bulletin of the Maryland Herpetological Society 21: 115-118.

Fritts, T. H., N. J. Scott Jr., and J. A. Savidge. 1987. Activity of the arboreal Brown Tree Snake (Boiga irregularis) on Guam as determined by electrical power outages. Snake 19: 51-58.

Hoser, R T. 1980. Further records of aggregations of various species of Australian snakes. Herpetofauna 12: 16-22.

Rodda, G. H., T. H. Fritts, M. J. McCoid, and E. W. Campbell. 1999. An overview of the biology of the brown treesnake (Boiga irregularis), a costly introduced pest on Pacific islands. Problem snake management: the habu and the brown treesnake. Cornell University Press, Ithaca, New York. pp. 44-80.

Savidge, J. A. 1986. The role of disease and predation in the decline of Guam's avifauna. Ph.D. diss., Univ. Illinois, Urbana-Champaign.

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Life Expectancy

Lifespan, longevity, and ageing

Maximum longevity: 13.1 years (captivity)
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Reproduction

While Boiga irregularis in Australia only reproduce during the wetter and warmer summer months (Shine 1991), they appear to reproduce year round in Guam (McCoid 1994). One major reason a reproductive season hasn't been established for Bo. irregularis in Guam is due to the rarity of finding pregnant females, probably owing to their inactivity and/or increased secretiveness (Fitch 1987).

Neither courtship nor mating has been observed in Boiga irregularis in the wild. In captivity, courtship proceeded with the male mounting the female, rubbing her body with his chin, and progressing in a jerky motion toward her tail while attempting to lift her tail with his own. Copulation has never been observed (Rodda et al. 1999). In Australia, females appear to lay eggs once a year, but nothing is known about their counterparts in Guam (Shine 1991). Few egg clutches have been found in Guam. It is likely that females lay eggs underground, as do females in Australia (Ehmann 1992). Clutch sizes range from 4 to 12 eggs (Zwinenberg 1978). Incubation times for Australian clutches range from 76 to 90 days, incubated at 25°C to 30°C, respectively. The incubation time for a Guam clutch was 94 days, incubated between 25° and 30°C, producing one live young (Rodda et al. 1999).

Boiga irregularis reach sexual maturity at three years of age (Fritts 1988).

References

Ehmann, H. 1992. Encyclopedia of Australian Reptiles. Pymble, N.S.W., Australia: Collins, Angus & Robertson.

Fitch, H. S. 1987. Collecting and life-history techniques. Snakes: Ecology and Evolutionary Biology. New York: Macmillan. pp. 143-164.

Fritts, T. 1988. The Brown Tree Snake, Boiga irregularis, A Threat to Pacific Islands. Fish and Wildlife Service Biological Report, Sept. (31).

McCoid, M. J. 1994. Boiga irregularis (Brown Tree Snake) reproduction. Herpetological Review 25: 69-70.

Rodda, G. H., T. H. Fritts, M. J. McCoid, and E. W. Campbell. 1999. An overview of the biology of the brown treesnake (Boiga irregularis), a costly introduced pest on Pacific islands. Problem snake management: the habu and the brown treesnake. Cornell University Press, Ithaca, New York. pp. 44-80.

Shine, R. 1991. Strangers in a strange land: Ecology of Australian colubrid snakes. Copeia 1991: 120-131.

Zwinenberg, A. J. 1978. Die Braune Nachtbaumnatter Boiga irregularis. Aquar. Terrar. Z. 31: 177-179.

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Molecular Biology and Genetics

Molecular Biology

Barcode data: Boiga irregularis

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 6 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

ACCCTATACCTATTATTTGGGGCATGATCAGGCCTAATCGGAGCTTGCTTA---AGCATCTTAATACGAATAGAACTAACACAACCAGGATCGCTCCTAGGAAGC---GATCAAATCTTTAATGTTCTAGTTACAGCCCATGCATTCATCATAATCTTCTTCATAGTCATACCAATCATGATTGGGGGATTTGGTAACTGATTAATCCCATTAATA---ATTGGAGCACCAGATATAGCCTTTCCTCGTATAAATAACATAAGCTTTTGATTATTACCACCAGCACTACTTCTTTTATTATCATCTTCATACGTTGAAGCCGGAGCAGGAACAGGATGAACTGTATACCCACCACTGTCCGGAAATCTAGTACACTCAGGTCCATCAGTAGACCTG---GCTATTTTTTCCCTACATCTAGCAGGCGCCTCCTCCATCCTGGGGGCAATTAATTTTATTACTACATGCATCAACATAAAACCCAAATCTATACCAATATTTAACATTCCATTATTTGTCTGATCAGTGTTAATTACTGCCATTATACTACTTCTCGCCTTGCCAGTATTAGCAGCA---GCAATCACCATACTACTAACCGACCGAAATCTTAACACTTCTTTCTTTGATCCCTGTGGGGGAGGTGACCCAGTATTATTCCAACACCTATTCTGA
-- end --

Download FASTA File
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Source: Barcode of Life Data Systems (BOLD)

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Statistics of barcoding coverage: Boiga irregularis

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 6
Specimens with Barcodes: 7
Species With Barcodes: 1
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© Barcode of Life Data Systems

Source: Barcode of Life Data Systems (BOLD)

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Relevance to Humans and Ecosystems

Risks

Since Boiga irregularis was introduced to Guam, circa 1950, it has been a destructive force on Guam's indigenous species. Boiga irregularis's population explosion, due to its lack of predators and generalist predation, has caused the extirpation of several native bird and lizard species (Rodda and Fritts 1992; Savidge 1987). Evidence of Boiga irregularis's role in species extirpations on Guam include the geographic patterning of bird losses mirroring the expansion of the snake, high densities of snake at the time of extirpation, the snake being the only known predator of some extirpated species, and a lack of other factors that would account of the extirpation (such as habitat destruction or environmental contaminents; Rodda et al. 1999).

References

Rodda, G. H., and T. H. Fritts. 1992. The impact of the introduction of the Brown Tree Snake, Boiga irregularis, on Guam's lizards. Journal of Herpetology 26: 166-174.

Rodda, G. H., T. H. Fritts, M. J. McCoid, and E. W. Campbell. 1999. An overview of the biology of the brown treesnake (Boiga irregularis), a costly introduced pest on Pacific islands. Problem snake management: the habu and the brown treesnake. Cornell University Press, Ithaca, New York. pp. 44-80.

Savidge, J. A. 1987. Extinction of an island forest avifauna by an introduced snake. Ecology 68: 660-668.

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Wikipedia

Brown tree snake

The brown tree snake (Boiga irregularis) is an arboreal rear-fanged colubrid snake native to eastern and northern coastal Australia, eastern Indonesia (Sulawesi to Papua), Papua New Guinea, and a large number of islands in northwestern Melanesia. This snake is infamous for being an invasive species responsible for devastating the majority of the native bird population in Guam.[1]

Diet[edit]

The brown tree snake preys upon birds, lizards, bats, rats, and small rodents in its native range.[2] It preys on birds and shrews in Guam.[3]

Due to the availability of prey and lack of predators in introduced habitats such as Guam, they have been known to grow to larger sizes than their normal 1 to 2 metres (3.3 to 6.6 feet) in length.[2] The longest recorded length of this species is one found on Guam measuring three metres (9.8 feet).[2]

Reproduction[edit]

The reproductive characteristics of the brown tree snake have not been widely studied.[2] The female is known to produce 4-12 oblong eggs, 42–47 mm (1⅝-1⅞ in.) long and 18–22 mm (⅝-⅞ in.) wide with leathery shells.[2] Females may produce up to two clutches per year depending upon seasonal variations in climate and prey abundance.[2] The female deposits the eggs in hollow logs, rock crevices, and other sites where they are likely protected from drying and high temperatures.[2] Populations on Guam may reproduce year round.[4]

Venom[edit]

Invasive species on Guam

The brown tree snake is a nocturnal, rear-fanged colubrid, possessing two small, grooved fangs at the rear of the mouth.[5] Due to the placement of the fangs and their grooved rather than hollow architecture, the venom is difficult to convey into a bite on a human, and thus is only delivered in small doses. The venom appears to be weakly neurotoxic and possibly cytotoxic with localized effects that are trivial for adult humans; serious medical consequences have been limited to children, who are more susceptible because of their low body mass.[2] The snake has been reported as aggressive,[2] but is not considered dangerous to an adult human.[5] The venom seems to be primarily used to subdue lizards, which can be more easily positioned in the rear of the mouth for venom delivery.[2]

brown tree snake, Queensland, in characteristic "S-posture"
Brown tree snake on a fence post on Guam
Brown tree snake on Guam

Invasive species[edit]

Shortly after World War II, and before 1952, the brown tree snake was accidentally transported from its native range in the South Pacific to Guam, probably as a stowaway in ship cargo.[2][5] As a result of abundant prey resources on Guam and the absence of natural predators outside of feral pigs and mangrove monitors, brown tree snake populations reached unprecedented numbers.[2] Snakes caused the extirpation of most of the native forest vertebrate species; thousands of power outages affecting private, commercial, and military activities; widespread loss of domestic birds and pets; and considerable emotional trauma to residents and visitors alike when snakes invaded human habitats with the potential for envenomation of small children.[2] Since Guam is a major transportation hub in the Pacific, numerous opportunities exist for the brown tree snakes on Guam to be introduced accidentally to other Pacific islands as passive stowaways in ship and air traffic from Guam.[2] To minimize this threat, trained dogs are used to search, locate, and remove brown tree snakes before outbound military and commercial cargo and transportation vessels leave the island.[6] Numerous sightings of this species have been reported on other islands including Wake Island, Tinian, Rota, Okinawa, Diego Garcia, Hawaii, and even Texas in the continental United States.[7] An incipient population is probably established on Saipan.[2] Acetaminophen has been used to help eradicate the snake on Guam.[8]

Underlying biology[edit]

General characteristics[edit]

The brown tree snake (Boiga irregularis) is a nocturnal, arboreal species that uses visual and chemical cues in hunting in the tropical rainforest canopy and/or on the ground .[9] It is a member of the subfamily Colubrinae, genus Boiga, which is a group of roughly twenty five species that are referred to as “cat-eyed” snakes for their vertical pupils.[10] The brown tree snake is generally between one and two meters (three and six feet) in length in its native range. The snake is long and slender, which facilitates its climbing ability and allows it to pass through tiny spaces in buildings, logs, and other shaded locations where it seeks refuge during daylight hours. Variations in coloration occur in the snake’s native range, ranging from a lightly patterned brown to yellowish/green or even beige with red saddle-shaped blotches.[10] They are rear-fanged, have a large head in relation to their body, and can survive for extended periods of time without food.[10]

Reproductive behaviour[edit]

The reproductive characteristics of the brown tree snake are not well known. On average the female produces 4-12 oblong eggs, 42–47 mm long and 18–22 mm wide. The eggs have a leathery shell and as such, the female deposits her eggs in refugia such as hollow logs, rock crevices, and other sites where they are likely protected from drying and high temperatures.[11] Females may produce two clutches per year, but the timing of said clutches may depend on seasonal variations in climate and prey abundance. If conditions for bearing eggs are not hospitable, the female brown tree snake is able to store sperm and produce the eggs several years after mating.[10]

Predatory behaviour[edit]

The brown tree snake is a generalist feeder known to eat a wide variety of foods, when threatened is highly aggressive and tends to lunge and strike the aggressor repeatedly. The snake has numerous teeth but only the last two on each side of the upper jaw have grooves, which inject venom as it bites. Therefore, the snake’s mouth must be opened as wide as possible to insert and expose their fangs. A chewing movement is used by the snake to inject the venom by means of capillary action along the grooved fangs. The venom is used to subdue and kill prey on which the snake feeds however the venom is not considered dangerous to adult humans. In addition to subduing its victim with its venom, the brown tree snake often wraps its body around the prey, like a constrictor, to immobilize the prey while chewing and consuming the animal .[2]

Native habitat[edit]

The brown tree snake is native to coastal Australia, Papua New Guinea, and a large number of islands in northwestern Melanesia. The species occurs on variably sized islands, extending from Sulawesi in eastern Indonesia through Papua New Guinea and the Solomon Islands and into the wettest coastal areas of Northern Australia.[9] The snakes on Guam represent the only documented reproductive population outside the native range.

Current habitats[edit]

The brown tree snake is not restricted to forested habitats but can occur in grasslands and sparsely forested areas as well. In Papua New Guinea, it occupies a wide variety of habitats at elevations up to 1,200 m.[11] It is most commonly found in trees, caves, and near limestone cliffs but frequently comes down to the ground to forage at night. It hides during the day in the crowns of palm trees, hollow logs, rock crevices, caves, and even the dark corners of thatched houses near the roof.[9] Based on the frequency of sightings of this snake, in relation to buildings, poultry, and caged birds, the snake is considered to be common in human-disturbed habitats.[12]

Physiological evidence for reproductive suppression[edit]

Environmental stressors such as lack of shelter, climate change, overcrowding and loss of prey have been researched as primary causes of diminished snake density as they have been found to have direct correlation with the reproductive success of the snake. Current research on the breeding patterns of the brown tree snake is being conducted in hopes of further understanding how these environmental stressors are affecting the population density of the snake on Guam.[13]

A study conducted by I.T. Moore, predicted that low body condition would correlate to high levels of stress hormones and low levels of sex steroids in free living brown tree snakes on Guam when compared with the native snake population in Australia and snakes held in captivity on Guam.[13] After extensive research, it was found that the body condition in the free living snakes was significantly different than the body conditions of native and captive snakes.[13] The results determined that, “depressed body condition and elevated plasmacorticosteron levels in the free-living animals suggest that a lack of food resources was placing individuals under chronic stress resulting in suppression of the reproductive system.”[14] The study suggested that snakes living under stressful conditions such as high population densities or low prey resources had suppressed reproduction at multiple stages including steroidogenesis and gametogenesis.[14]

Current status[edit]

Currently, the brown tree snake population on Guam is declining with an equilibrium population size predicted to be roughly 30 to 50 snakes per hectare (2.5 acres).[15] The decline in snake population may be identified as a result of depleted food resources, adult mortality and/or suppressed reproduction.[15] That is, the brown tree snake population on Guam has exceeded the carrying capacity of the island.

Species status and effect[edit]

Effect of early introduction[edit]

The introduction of the brown tree snake on Guam after WWII has had a significant impact on the community dynamics of the island. Upon its introduction the brown tree snake population exploded and spread across the entirety of Guam. The brown tree snake population on the island has reached peak densities of greater than 100 snakes per hectare.[15] This population spike was caused by the copious amount of resources newly available to the brown tree snake upon its introduction. The limitations on the snake’s population in its native range is predominantly food based. The snake’s food source is far more limited in its native range than on the island of Guam as the prey in its natural range boasts significantly more natural defences to the snake than the prey on Guam.[11]

The predominant population affected by the snake's introduction was that of native bird species such as the Mariana fruit dove, the Guam flycatcher, the rufous fantail and the Micronesian myzomela. The introduction of the brown tree snake into Guam has resulted in extinction of twelve native bird species in total. The Guam National Wildlife Refuge is attempting to prevent the extinction of additional bird species endangered by the snake.[16] Other species significantly affected by the invasion of these snakes were small lizards and small mammals.[13] Research has indicated a direct correlation of the spread of these snakes across the island to the decrease in the populations of these native species. Furthermore, the introduction of the brown tree snake has had an indirect, negative impact on vegetative diversity as its intense predatory nature has decreased populations of vital pollinators including native birds and fruit bats.[15] Data collected from nearby islands lacking brown tree snake populations depict a significant difference in vegetative species richness, that is, islands close to and similar to Guam in which the brown tree snake has not been introduced have greater vegetative species diversity.[15] Overall, the vertebrate fauna and native flora of Guam have suffered tremendously because of the introduction of the brown tree snake.[15]

Population control methods[edit]

Predation on brown tree snakes[edit]

An investigative study was performed to find predators of the brown tree snake that could possibly serve as a population control method.[17] In this study two actual predators were identified and 55 potential predators were identified: the two actual predators identified were the red-bellied black snake and the cane toad.[17] Actual predators were identified by evidence showing that they would actually prey upon and consume the brown tree snake in a natural habitat whereas potential predators were identified as species that were only physically capable of consuming the brown tree snake.[18] The research collected in this study suggested that even with the introduction of brown tree snake predation, it was unlikely this would serve as an effective brown tree snake population control method.[17] One reason for this conclusion was that the identified actual predators of the brown tree snake are generalist feeders and would cause further detriment to other native island species.[18]

Another possible negative outcome of introducing species as a control method for the brown tree snake population is predation on juvenile cane toads and red-bellied snakes by brown tree snakes themselves, because they are opportunistic and generalist feeders.[18] This investigation determined that the environmental and ecological risk associated with the introduction of these predators was too high to implement.[17] Lastly, red-bellied snakes could pose a threat to the health of humans. The cost of introduction of such predatory species outweighs the benefits and is not practical.

Capturing methods[edit]

Given the environmental impact of the brown tree snake, studies have attempted to provide a capturing methodology to alleviate the detrimental effects of the tree snake. The use of mice as bait has shown considerable reduction effects when combined with acetaminophen in a mark-recapture experiment leading to potential widespread application in Guam. When utilizing a precisely defined treated plot with results corrected for immigration and emigration, the additive effect of both acetaminophen and mice usage shows a 0% survival rate of the brown tree snake. In the study, 80 mg of acetaminophen was inserted into mouse carcasses.[14] In addition, one study showed that increasing inter-trap spacing would not only increase efficiency, but also not compromise efficacy as 20-, 30-, and 40-meter long perimeter trap lines were compared and no difference was found.[19] Another study echoed the aforementioned notion of increasing inter-trap spacing.[19]

References[edit]

  1. ^ Invasive Species: Animals - Brown Tree Snake, National Agricultural Library, United States Department of Agriculture, Retrieved 2010-08-31
  2. ^ a b c d e f g h i j k l m n o p Fritts, T.H.; D. Leasman-Tanner (2001). "The Brown Treesnake on Guam: How the arrival of one invasive species damaged the ecology, commerce, electrical systems, and human health on Guam: A comprehensive information source". U.S. Department of the Interior. Retrieved 2008-09-11. 
  3. ^ Pianka, Eric R.; King, Dennis; King, Ruth Allen. (2004). Varanoid Lizards of the World. Indiana University Press, 588 pages ISBN 0-253-34366-6
  4. ^ Savidge, Julie, Fiona Qualls, and Gordon Rodda. "Reproductive Biology of the Brown Tree Snake, Boiga Irregularis (Reptilia: Colubridae), During Colonization of Guam and Comparison with That in Their Native Range." Pacific Science, 61.2 (2007): 191-199.
  5. ^ a b c Mehrtens, John (1987). Living Snakes of the World in Color. New York: Sterling. ISBN 0-8069-6461-8. 
  6. ^ Vice, Daniel. "Working Dogs: The Last Line of Defense for Preventing Dispersal of Brown Tree Snakes from Guam". 
  7. ^ Kraus, Fred (2004). "ALIEN SPECIES". Department of Land and Natural Resources State of Hawaii. Retrieved 2008-09-11. 
  8. ^ Brad Lendon (2010-09-07). "Tylenol-loaded mice dropped from air to control snakes". cnn.com. Retrieved 2010-09-07. 
  9. ^ a b c Campbell, S.R.; S.P. Mackessy (2008). "Microhabitat use by Brown Treesnakes (Boiga irregularis): Effects of moonlight and prey.". 42(2):246-250. Journal of Herpetology. 
  10. ^ a b c d Fritts, T.H.; G.H. Rodda (1998). "The role of introduced species in the degradation of island ecosystems: A case history of Guam.". 29:113-140. Annual Review of Ecology and Systematics. 
  11. ^ a b c Bomford, M; F.Kraus (2008). "Predicting establishment for alien reptiles and amphibians: a role for climate matching.". 11:713-724. Biological Invasions. 
  12. ^ D'Evelyn, S.T.; N. Tauri (2008). "Learning-by-catching: Uncertain invasive-species populations and the value of information.". 89(4):284-292(2). Journal of Environmental Management. 
  13. ^ a b c d Moore, I.T..; M.G. Greene (2005). "Physiological evidence for reproductive suppression in the introduced population of brown tree snakes (Boiga irregularis) on Guam.". 121(1):91-98. Biological Conservation. 
  14. ^ a b c Savarie, P.J.; J.A. Shivik (2001). "Use of acetaminophen for large-scale control of brown tree snakes". 65(2):356-365. Journal of Wildlife Management. 
  15. ^ a b c d e f Mortensen, H.S.; Y.L. Dupont (2008). "snake in paradise: Disturbance of plant reproduction following extirpation of bird flower-visitors on Guam.". 141(8):2146-2154. Biological Conservation. 
  16. ^ Maxfield, Barbara (2009-07-22). Guam National Wildlife Refuge Draft Comprehensive Conservation Plan Released for Public Review and Comment. US Fish and Wildlife Service. Retrieved 2012-02-21. 
  17. ^ a b c d Caudell, J.N.; M.R. Conover (2001). "Predation of brown tree snakes (Boiga irregularis) in Australia.". 49(2-3):107-111. ." International Biodeterioration & Biodegradation. 
  18. ^ a b c Burnett, K.M.; S. D'Evelyn (2008). "Beyond the lamppost: Optimal prevention and control of the Brown Tree Snake in Hawaii". 67(1):66-74. Ecological Economics. 
  19. ^ a b Engeman, R.A.; M.A. Linnell (2003). "The effect of trap spacing on the capture of brown tree snakes on Guam". USDA National Wildlife Research Center. 
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