Boiga irregularis

Geographic Range

Boiga irregularis , brown tree snakes, are native to northern Australia (New South Wales, Northern Territory, and Queensland), Papua New Guinea, and eastern Indonesia. They have also been accidentally introduced to the Pacific island of Guam (Savidge et al., 2007).

• Biogeographic Regions
• australian australian
  • native native
• pacific ocean pacific ocean
  • introduced introduced

Habitat

The Brown Tree Snake prefers the lowland woodlands and coastal forests of Northern Australia as well as the more tropical rainforests of Papua New Guinea and Indonesia. However, they are not restricted to forests and have been observed to live in caves and human made structures (i.e. attics, upper portions of buildings, etc.) as well. This snake is often nocturnal and generally takes shelter in hollow logs, tree crowns, caves, or miscellaneous crevices during the day.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest
• rainforest rainforest

• Other Habitat Features
• urban urban
• suburban suburban
• estuarine estuarine
• caves

Physical Description

The Brown Tree Snake has a very slender and agile body coinciding with its arboreal lifestyle. They generally are a light brown with either darker dorsal markings or a uniform coloration, however, these snakes have also been observed to be red, yellow, pink, or a creamy white. It has a distinctively large head with opisthoglyphous (rearward) fangs and big bulbous eyes characteristic of the genus Boiga (and in keeping with nocturnal habits). They are long, laterally compressed snakes (2 to 2.5 m long) with large vertebral scales and a long tail. Mature Brown Tree Snakes have variable masses ranging anywhere from 60 to 2300 g.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• venomous venomous

• Sexual Dimorphism
• male larger

Development

As with all squamates, fertilization is internal. Shelled amniotic eggs are laid; the hatchling snakes are essentially miniatures of the adults and grow incrementally. Sex is probably determined genetically, as appears true for all snakes. It is unknown whether Brown Tree Snakes have indeterminate growth.

Reproduction

These snakes appear to reproduce year-round, but more research is needed on Brown Tree Snake mating systems.

Male Brown Tree Snakes have been observed to store sperm year-round suggesting aseasonal spermatogensis; however, this is under debate due to the fact that the majority of tropical snakes have seasonal spermatogensis (Mathies et al., 2010). Females have been observed to lay clutches of 3-12 leathery-shelled eggs biannually. Generally, females lay their eggs in hollow logs, rock crevices, or caves in order to protect them from desiccation (Fritts & Rodda, 1998). Eggs hatch after approximately 90 days and offspring are around 50 cm long and take around 3 or 4 years to reach sexual maturity (Savidge et al., 2007).

• Key Reproductive Features
• year-round breeding year-round breeding
• sexual sexual
• oviparous oviparous

Brown Tree Snakes abandon their eggs after laying and there is no parental care of the young.

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning
  • protecting
    • female

Lifespan/Longevity

Brown Tree Snakes are reported to have a lifespan ranging from 10-15 years (Amand, 2000).

Behavior

Brown Tree Snakes are largely arboreal but have been observed living in non-arboreal situations. They are nocturnal, spending the daytime sheltered in trees, caves, or cliffs and the nighttime hunting and foraging (Campbell et al., 2008). They are also known to be very aggresive towards any potential predator that comes within close proximity (O'Shea & Halliday, 2001).

• Key Behaviors
• arboreal arboreal
• nocturnal nocturnal
• motile motile

Communication and Perception

These snakes undoubtedly have fairly good eyesight, but will predictably depend on detecting chemical cues (odors) via the vomero-nasal ("Jacobson's") organ as in other snakes. Perception of sound has not been studied in this species. More research is needed specifically on Brown Tree Snake communication and perception.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• visual visual
• tactile tactile
• vibrations vibrations
• chemical chemical

Food Habits

The Brown Tree Snake eats a wide variety of prey ranging from birds, small mammals, amphibians,and other reptiles. This snake subdues its prey either through the use of its venom or through constricting its prey with its long body (Amand, 2000). In Guam, the Brown Tree Snake is invasive and is believed to have caused the extinction of several bird species, and has greatly reduced populations of other vertebrates (O'Shea & Halliday, 2001).

• Primary Diet
• carnivore carnivore
  • eats terrestrial vertebrates

• Animal Foods
• birds
• mammals
• amphibians
• reptiles

Predation

In their natural range, Brown Tree Snakes are eaten by wild pigs, birds of prey, and certain other snakes and large lizards, such as monitors. There are few known predators of this snake on the island of Guam, which has allowed the species there to attain abnormally large population density and to grow to larger than average size (Up to 3 m; O'Shea & Halliday, 2001). Brown Tree Snakes are rear-fanged and venomous, and are cryptically colored to hide in vegetation.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

The Brown Tree Snake is a predator that has normal constraints on its populations in its natural range. It has no natural predators on the island of Guam and therefore has become an apex predator. Because of this, Brown Tree Snakes have become overabundant there and have severely disrupted the ecosystem primarily through its predatory impacts on native vertebrate species (Amand, 2000) (Fritts & Rodda, 1998).

Economic Importance for Humans: Positive

The Brown Tree Snake provides no specific benefit towards humans, though in its natural habitat it contributes to a functioning ecosystem.

Economic Importance for Humans: Negative

Brown Tree Snakes are mildly venomous to humans; bites can be painful and occasionally debilitating. Bites to children or infants can be more serious. Where introduced, as on Guam, in addition to ecological damage, this snake can cause power outages by hiding in transformers, and detracts from tourism. Significant economic investments have been made in Guam to eradicate this invasive species from the island.

• Negative Impacts
• injures humans
  • bites or stings
  • venomous venomous
• household pest

Conservation Status

Brown tree snakes are not considered threatened or endangered. Where they have been introduced, they pose a substantial threat to native faunas and eradication programs are active.

Additional Links

Encyclopedia of Life

Contributors

Stephen Kerr (author), Michigan State University, James Harding (editor), Michigan State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Amand, A. 2000. Boiga irregularis (Brown Tree Snakes) on Guam and Its Effect on Fauna. Restoration and Reclamation Review , 6/6: 1-6.

Campbell, S., S. Mackessy, J. Clarke. 2008. Microhabitat Use by Brown Treesnakes (Boiga irregularis) Effects of Moonlight and Prey. Journal of Herpetology , 42/2: 246-250.

Fritts, T., G. Rodda. 1998. THE ROLE OF INTRODUCED SPECIES IN THE DEGRADATION OF ISLAND ECOSYSTEMS: A Case History of Guam. Annu. Rev. Ecol. Syst. , 29: 113-140.

Mathies, T., J. Cruz, V. Lance, J. Savidge. 2010. Reproductive Biology of Male Brown Tree Snakes (Boiga irregularis) on Guam. Journal of Herpetology , 44/2: 209-221.

O'Shea, M., T. Halliday. 2001. Reptiles and Amphibians . United States: Dorling Kindersley.

Savidge, J., F. Qualls, G. Rodda. 2007. 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: 191-199.