Brown tree snake

The brown tree snake is a nocturnal, arboreal species that uses both visual and chemical cues when hunting, whether in the rainforest canopy or on the ground. 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. The brown tree snake is generally 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. Variations in coloration occur in the snake's native range, from lightly patterned brown to yellowish/green or even beige, with red, saddle-shaped blotches. They are rear-fanged, have a large head in relation to their body, and can survive for extended periods of time without food. Owing to the availability of prey and the lack of predators in introduced habitats such as Guam, they have been known to grow to larger sizes than their typical 1 to 2 m (3.3 to 6.6 ft) in length. The longest recorded length of this species is one found on Guam measuring 3 m (9.8 ft). == Distribution and habitat ==

The brown tree snake is native to coastal Australia, Papua New Guinea, and many 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. A separate species, Boiga flavescens, was described from Sulawesi in the nineteenth century. Subsequent authors identified both B. flavescens and B. irregularis on the island, and flavescens was synonymised with irregularis in 1985 by In den Bosch. Weinell et al. found significant DNA differences between the Sulawesi and Sundaland populations, proposing in 2021 that all members west of Weber's Line be designated B. flavescens. The brown tree snake is not restricted to forested habitats; it also occurs in grasslands and sparsely forested areas. In Papua New Guinea, it occupies a wide variety of habitats at elevations up to 1,200 m. 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. Although the snake has been found in nearly all habitats on the island, it is most common in primary and secondary forest habitats on Guam. ==Diet==

and its chick while feeding on another chick. In Queensland. In its native range, the brown tree snake preys upon birds, lizards, bats, and mice and other small rodents. The larger snakes are often seen shifting their diet towards endotherms rather than consuming ectotherms due to relative prey size. ==Behavior==

Reproduction The reproductive characteristics of the brown tree snake have not been widely studied. Unlike the native population in Australia, populations in Guam may reproduce year-round, as there is no evidence of seasonality in the population. Male courtship behaviour involves tongue-flicking, head-jerking, and chin-rubbing on the female in preparation of mating. If females are receptive, mating will take place almost immediately. This novel form of movement has been observed to be physically demanding, as snakes seen utilising it make frequent stops and move more slowly than other forms of locomotion. This is indicative of shifts in snake behaviour or movement across the year, and may partially be driven by differences in seasonal detection probability. Potentially, during months of low activity, brown tree snakes may remain in tree canopies, where detection by the public is unlikely. ==Venom==

The brown tree snake is a nocturnal, rear-fanged colubrid, possessing two small, grooved fangs at the rear of the mouth.{{cite book |last= Mehrtens|first= John|title= Living Snakes of the World in Color|url= https://archive.org/details/livingsnakesofwo00mehr|url-access= registration|year= 1987|publisher= Sterling ==Invasive species==

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 or by crawling into the landing gear of Guam-bound aircraft. As a result of abundant prey resources on Guam and the absence of natural predators apart from the native Mariana monitor and feral pigs, brown tree snake populations reached unprecedented numbers. 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 people's pets; and considerable emotional trauma to residents and visitors alike when snakes invaded human habitats with the potential for envenomation of small children. To minimise 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. 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. Hawaii is especially at heavy risk from the snake, as direct military flights between Guam and Hawaii are allowed. Brown tree snakes are regularly intercepted at landing areas. A successful introduction could pose an immense threat to the already highly threatened endemic birds of the islands. An incipient population was thought to be established on Saipan after sightings around the port; Physiological evidence for reproductive suppression Environmental stressors such as lack of shelter, climate change, overcrowding, and loss of prey have been studied as primary causes of diminished snake density, as they correlate directly with snakes' reproductive success. 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. 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. After extensive research, the body condition of free-living snakes was found to differ significantly from that of native and captive snakes. Current status Currently, the brown tree snake population on Guam is declining with an equilibrium population size predicted to be roughly . The decline in snake population may be identified as a result of depleted food resources, adult mortality, and/or suppressed reproduction. The brown tree snake population on Guam has exceeded the carrying capacity of the island. Species status and effect Effect of early introduction The introduction of the brown tree snake to Guam after WWII has had a significant impact on the island's community dynamics. Upon its introduction, the brown tree snake population exploded and spread across Guam. The brown tree snake population on the island has reached peak densities exceeding . Other species significantly affected by the invasion of these snakes were small lizards and small mammals. Overall, the vertebrate fauna and native flora of Guam have suffered tremendously because of the introduction of the brown tree snake. The outages, depending on the scale, can cause millions of dollars of revenue loss to Guam and can affect either the whole island or smaller parts of it. According to a study by Thomas H. Frittz, there were an average of 133 power outages per year from 1991 to 1997 caused by the brown tree snake. A majority of these outages were considered major disruptions to the island's power grid. Population control methods Due to the success of the brown tree snakes on Guam, there have been many efforts to eradicate the invasive population and prevent its spread to other places, including the mainland United States and other islands, such as Hawaii. Other goals for controlling this species include intercepting snakes that are either coming to or leaving Guam, such as those that stow away on planes, protecting sensitive areas on Guam from further destruction, and exterminating any other populations that exist outside their native range. To support these initiatives, the National Wildlife Research Center (NWRC) has received long-term funding since 1995 from the Department of Defense's Legacy Resource Management Program, which supports conservation projects on military properties across the U.S. These lands which are home to endangered species and delicate ecosystems benefit from efforts that balance ecological preservation with national defense operations. Additional funding has come from the Department of Interior's Office of Insular Affairs. Current control techniques and search methods for the brown tree snake include trapping, spotlight searches, baiting and poisoning, the use of search dogs, barriers, fumigation, and reducing prey availability. More recently, in 2021, the Department of the Interior announced an additional $4.1 million to support control efforts across the Pacific region. These funds are being used to implement interdiction at ports, expand canine inspection units, and support rapid response activities, especially in high-risk areas like Saipan, Tinian, and Cocos Island. Capturing and poisoning methods tablets, designed to catch on trees in areas where brown tree snakes are invasive Given the environmental impact of the brown tree snake, studies have attempted to develop a capture methodology to mitigate its detrimental effects. The use of mice as bait has shown considerable reduction effects when combined with acetaminophen, to which the snake is particularly sensitive, in a mark-recapture experiment leading to potential widespread application in Guam. When utilising 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. Another study echoed the aforementioned notion of increasing inter-trap spacing. In a large-scale field trial initiated in 2013, scientists deployed these toxic mouse baits via aerial drop across two separate forest plots on Guam. A third site of equal size was left untreated to serve as a control. Throughout the 16-month experiment, the National Wildlife Research Center (NWRC) tracked both snake and rodent populations to evaluate the baiting strategy's effectiveness and whether it caused any unintended environmental impacts. Further fieldwork highlighted similar limitations. When a new population of brown tree snakes was discovered in 2020 on Cocos Island, researchers explored various control methods, including cage trapping and acetaminophen-laced carrion baits placed both on the ground and suspended in trees. Despite more than 2,400 bait nights and 10,000 trap nightsmonitored with time-lapse camerasno baits were consumed, and only a single snake was trapped. These findings suggested that traditional baiting and trapping methods were ineffective in that environment. Scientists attributed the failure not to snake scarcity but to the abundance of preferred natural prey, such as large geckos and birds. As a result, researchers plan to continue manual removal efforts and to explore whether live bird lures might prove more effective in future attempts. Predation on brown tree snakes An investigation was conducted to identify predators of the brown tree snake that could serve as a means of population control. In this study, two actual predators and 55 potential predators were identified: the two actual predators were the red-bellied black snake and the cane toad. 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. 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. Using both dead and live snakes, the study looked for evidence of wounds and how they affected the snake's bodies as well as the live snake's reactions after being shot. The study found that higher-powered guns with larger ammunition were preferable for controlling brown tree snakes. == References ==