Brown night tree snake
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Brown night tree snake ( Boiga irregularis ) |
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| ( Merrem in Bechstein , 1802) |
The brown tree snake ( Boiga irregularis ) is an on New Guinea , the Solomon Islands , many islands of the South Pacific as well as in Australia domestic viper of genus boiga ( Boiga ). Like the other kinds of the genus is the snake toxic, so is commonly the illusion snakes assigned. As a neozoon with a strongly negative effect on the ecosystem of various islands, especially on Guam , it is classified as an invasive species .
features
Build and size
In proportion to the body, the head is very broad and distinctly set off; however, the head is not unusually large for a snake of this length, rather the body is unusually slender. The snout is short and the pupils are slit-shaped , typical of nocturnal scaled reptiles. The proportionally large eyes, which protrude particularly in young animals, gave the brown night tree snake in Australia the colloquial name Doll's Eye ("doll 's eye "). The tail makes up only 21% of the total length and is therefore relatively short for arboreal snakes. No gender dimorphism is evident in the body proportions .
The body size, however, is very different between the sexes. The largest male ever measured in Guam was approx. 3.1 m long, the longest known female only 1.9 m. However, these are exceptions, the average length of the males on Guam is 2.1 m, that of the females 1.5 m. In addition, the population on Guam is apparently larger than average - the longest known male from Australia was only around 1.8 m long. The weight is comparatively low due to the slim build. For 1 m long specimens, it is 1 kg on average.
The teeth are of medium length. The rearmost teeth in the upper jaw are elongated and have a groove for poison transmission (opistoglyph teeth). Therefore, the brown night tree snake belongs to the snakes, which, however, are not a monophyletic taxon.
coloring
The specific epithet irregularis ("irregular") refers to the extremely variable coloration of the species. Usually the species shows a variable, uniform shade of brown. In quite a few copies there is an indistinct to clearly delimited, dark band markings. However, in Australia the banding can also be white, red, or blue.
Scaling
Brown night tree snakes almost always have only one preocular , on the Solomon Islands occasionally also two; Postoculars are always available. The frontal is about as far from the tip of the snout as it is long. There are also 1–4 temporals, 8–12 supralabials and 10–16 infralabials as well as a Loreal scale that separates the nasals from the preoculars. 17-25 rows of scales are formed across the middle body, less on other parts of the body. The anal is mostly undivided, in New Guinea night tree snakes have been found with both divided and undivided anals. There are 65–130 subcaudals. They are shared in all brown night tree snakes in the Solomon Islands and most specimens in Australia, otherwise they are not shared.
For the terminology of the scales see also the article Snake scaling .
distribution and habitat
The species is the most southern and eastern representative of the night tree snake. The westernmost occurrences are on the Moluccas , and east of the Wallace Line the range extends over Sulawesi , New Guinea and the northern and eastern parts of Australia to the Solomon Islands . However, brown night tree snakes are absent from the Lesser Sunda Islands . The species is most common in warm, humid forests and rainforests, but it also occurs in grass and bush landscapes, albeit much less frequently. Brown night tree snakes also penetrate suburban and urban areas. The distribution is limited by climatic factors: In Australia the snake does not penetrate inland or to the west because it is too dry and too hot there. The southernmost limit of distribution in Australia is near Sydney , where frost can occur for the first time. In New Guinea it occurs up to an altitude of 1375 m , above which the possibility of frost sets in.
nutrition
Brown night tree snakes are not food specialists and feed on lizards, frogs, small mammals ( rodents and bats ), birds and bird eggs. Young animals prefer small lizards, while the adult snakes prey on endothermic prey (mammals, birds). Large night tree snakes on large islands or on the mainland (New Guinea, Australia) primarily hunt mammals, while large specimens on small islands mostly prey on birds. This is probably related to the availability of the respective prey in the habitat. On Guam, almost no birds were found in the stomachs of brown night tree snakes in the rainforest, as they are almost completely extinct. The absolute majority now make up small lizards, mostly small geckos , as well as the snake introduced anoles and in snakes hunting on the ground, especially the skink Carlia fusca . In urban habitats, the proportion of birds (often chickens and chicks) and mammals such as rats is increasing again because these species can assert themselves better here or find better living conditions.
The brown night snake looks for food at night, mostly in trees. Only very large specimens look for food on the ground, possibly because they are too clumsy to hunt trees. Fast, active prey like geckos and rats are ambushed. Brown snakes are very happy to attack diurnal lizards that sleep on trees without cover - the lizards that occur naturally in the night tree snake therefore usually look for hiding places. The red throated anole, which has also been introduced to Guam, is one of the most important prey animals, as it sleeps without cover and does not notice approaching snakes. In some regions of Guam it can only be found in urban areas. In order to find inactive lizards and bird eggs, the snakes slowly crawl and lick large areas.
The poison generally does not play a role in catching prey; small prey are swallowed directly, large prey strangled. As the large eyes suggest, visual perception plays an important role in the hunt in addition to the tongue of the night tree snake.
The night tree snake can devour prey of up to 70% of its own weight and needs around 40% of its own weight in food per month.
Meaning as a neozoon
The night tree snake was introduced by humans to some Pacific islands, where it spread due to a lack of enemies and is considered an invasive species. After the introduction to Guam, probably through troop transports during the Second World War , the lack of natural enemies led to a strong increase in snakes. Today about 10,000 to 13,000 individuals of this species live on the island per square kilometer. This had a devastating effect on the fauna and flora of the island: within a few years most of the bird species and other small animals of the island that were considered prey of the snake were extinct . To date (as of 2008) ten of the twelve bird species resident in Guam have become extinct, the two remaining species have each been decimated to fewer than 200 specimens by the harmful effects of the snake. As a result of the far-reaching extinction of birds, the flora of Guam is now also threatened, as birds play a decisive role in the spread of their seeds for a large part of the plants . Attempts are made to fight the snakes with dead mice thrown from helicopters. These baits are provided with paracetamol beforehand ; the active ingredient is fatal to snakes even in small doses, and death occurs largely painlessly.
The brown night tree snake was also introduced into Hawaii before 1980 , where it is also a threat to indigenous animals; The cost of damage to electrical installations caused by snakes alone exceeded approximately $ 4.5 million annually in the period 1978–1997.
Snake venom
The brown night tree snake is poisonous like the other species of night tree snake . Your teeth in the back of the upper jaw are enlarged and provided with a groove for the poison from the poison glands (ophistoglyph poisonous teeth). The snake is known to be aggressive and often bites without warning when threatened and mostly withdraws immediately afterwards.
The poison is a neurotoxin , which can lead to mild paralysis and ptosis in humans . In most cases, however, only local symptoms at the bite site ( swelling , pain) are observed. No deaths are known.
literature
- GH Rodda et al .: An Overview of the Biology of the Brown Tree Snake (Bioga irregularis), a Costly Introduced Pest on Pacific Islands . In: GH Rodda, Y. Sawai, D. Chiszar & Hiroshi Tanaka (eds.): Problem Snake Management: The Habu and Brown Treesnake . Cornell University Press, Ithaca 1999, ISBN 0801435072 ( full text (PDF file; 2.96 MB)).
- Gordon H. Rodda, Julie A. Savidge: Biology and impacts of Pacific island invasive species. 2. Boiga irregularis, the brown tree snake (Reptilia: Colubridae) 1. In: Pacific Science Volume 61, No. 3, 2007, pp. 307-324 (PDF file; 526 kB).
Web links
- Boiga irregularis in The Reptile Database
- Entry in the Global Invasive Species Database
- Species profile at the United States Department of Agriculture (with additional literature)
Single receipts
- ↑ a b c d e f g Gordon H. Rodda, Julie A. Savidge: Biology and impacts of Pacific island invasive species. 2. Boiga irregularis, the brown tree snake (Reptilia: Colubridae) 1. In: Pacific Science Volume 61, No. 3, 2007, pp. 307-324 (PDF file; 526 kB).
- ↑ a b c d e f g G. H. Rodda et al .: An overview of the biology of the brown tree snake (Bioga irregularis), a costly introduced pest on Pacific Islands . In: GH Rodda, Y. Sawai, D. Chiszar, Hiroshi Tanaka (eds.): Problem Snake Management: The Habu and Brown Treesnake . Cornell University Press, Ithaca 1999, ISBN 0801435072
- ↑ NL Anderson et al .: Thermoregulation in a nocturnal, tropical, arboreal snake . In: Journal of Herpetology Volume 39, No. 1, 2005, pp. 82-90.
- ↑ Sarah Lowe, M. Browne, S. Boudjelas, M. De Poorter: 100 of the world's worst invasive alien species: a selection from the global invasive species database. ( Page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. 2000, accessed February 9, 2017.
- ↑ a b Hawaii Invasive Species Council: Brown tree snake , accessed February 9, 2017.
- ↑ JE Hill et al. , in a contribution to the Annual Meeting of the Ecological Society of America , Milwaukee, 2008. See also: The Guam Terror Snake. On: Wissenschaft.de from August 9, 2008.
- ↑ JA Shivik, PJ Savarie, L. Clark: Aerial delivery of baits to brown treesnakes . In: Wildlife Society Bulletin Volume 30, No. 4, 2002, pp. 1062-1067.
- ^ Mice join the fight against invasive snakes on Guam
- ↑ University of Adelaide, Clinical Toxinology Resources: Boiga irregularis (accessed July 8, 2018)
