Tiger snake (N. scutatus) — a highly venomous species found in the southern regions of Australia, including offshore islands such as Tasmania. These snakes are highly variable in color and get their name from the tiger-like stripes all over their body. All populations belong to the genus Notechis. They are sometimes described as separate species and/or subspecies. This snake is usually calm, like most snakes, and retreats when a person approaches, but when cornered, it releases poison, which is very dangerous for humans.
View origin and description
The genus Notechis (snakes) is in the aspid family. A 2016 genetic analysis showed that the closest relative of tiger snakes (N. scutatus) is the rough-scaled snake (Tropidechis carinatus). In the past, two species of tiger snake were widely recognized: the Eastern tiger snake (N. scutatus) and the so-called Black tiger snake (N. ater).
However, the morphological differences between the two seem to be inconsistent, and recent molecular studies have shown that N. ater and N. scutatus are genetically similar, so it would seem that there is currently only one widespread species that varies greatly in size and coloration.
Video: Tiger snake
Despite a recent revision, the old classification is still widely used and a number of subspecies are recognized:
- N. ater ater — Krefft's tiger snake;
- N. ater humphreysi — Tasmanian tiger snake;
- N. ater niger — peninsular tiger snake;
- N. ater serventyi — island Tiger snake from Chappell Island;
- N. scutatus occidentalis (sometimes N. ater occidentalis) — western tiger snake;
- N. scutatus scutatus — eastern tiger snake.
The modern fragmentary distribution of tiger snakes is associated with recent climate changes (increased aridity) and sea level changes (islands cut off from the mainland in the last 6000-10000 years). Populations isolated as a result of these events have undergone changes in their color schemes, sizes and ecological features in response to various environmental factors.
Appearance and features
The name tiger snake refers to the prominent yellow and black transverse stripes typical of some populations, although not all individuals have this coloration. The colors of the snakes range from dark black to yellow/orange with gray stripes to sandy gray without stripes. There are unconfirmed reports of pot-bellied tiger snakes in northeastern Tasmania.
Typical forms — black snake without stripes or faintly yellow to cream stripes. The most common form is dark olive brown or black brown, with off-white or yellowish stripes that vary in thickness. In striped populations, completely colorless individuals can be found. Some populations consist of almost completely disjunct members of the species, such as those in the central highlands and southwest Tasmania.
Interesting fact: The color mechanism evolves most strongly in populations exposed to highly variable weather and cool extremes, such as those experienced at high altitudes or offshore islands.
The head of the tiger snake is moderately wide and blunt, it differs little from the strong muscular body. The total length is usually about 2 meters. The belly is pale yellow, white or grey. Male tiger snakes are larger than females and have larger heads. The median scales consist of 17-21 rows, and the ventral scales 140-190 are often edged in black. There are also single anal and subcaudal scales on the underside of the tail.
Where does the tiger snake live?
This species is unevenly distributed over two broad areas: southeastern Australia (including the Bass Strait Islands and Tasmania) and southwestern Australia. In addition to mainland Australia, these snakes have been found on the following islands: Babylon, Cat Island, Halkey Island, Christmas Island, Flinders Island, Forsyth Island, Great Dog Island, Hunter Island, Shamrock Island and others. The distribution area of the species also includes the Savage River National Park, to Victoria and New South Wales. Its general habitat includes mostly the coastal regions of Australia.
Fun Fact: It is not clear whether the population of Karnak Island is entirely indigenous or not, as a large number of individuals were released on the island approximately in 1929.
Tiger snakes are found in coastal environments, wetlands, and streams, where they often form hunting territories. Areas where there is an abundance of foraged food can support large populations. This species is often associated with aquatic environments such as streams, dams, runoffs, lagoons, wetlands, and swamps. They can also be found in highly degraded areas, such as grasslands, especially where there is water and grass cover.
Tiger snakes will take shelter under fallen wood, in deep tangled vegetation, and in unused animal burrows. Unlike most other Australian snakes, tiger snakes are good at climbing both trees and man-made buildings, and have been found up to 10 m above the ground. The highest point above sea level where tiger snakes have been recorded is located in Tasmania at more than 1000 m.
What does a tiger snake eat?
These reptiles raid bird nests and climb trees up to 8 m high. A good indicator of the presence of a tiger snake is the alarming sounds of small birds such as shortbeaks and birds from the honeybear family. Juvenile tiger snakes will use constriction to subdue the struggling skink lizards that make up the primary food for small snakes.
They mainly hunt for prey during the daytime, but will also forage on warm evenings. These reptiles willingly look for food under water and can stay there for at least 9 minutes. As the size of the snake increases, so does the average size of the prey, however, this increase is not achieved due to the fact that larger snakes refuse small prey, if large food is not found, the tiger snake can be satisfied with a smaller representative of the fauna.
In the wild, tiger snakes have a wide dietary diversity including:
- small snakes;
- small mammals;
A bat was found in the stomach of one museum specimen, demonstrating the ability of a tiger snake to climb. Invertebrates have also been found in the stomachs of tiger snakes, however they could be taken as part of the carrion. Other taxa such as grasshoppers and moths may have been consumed as prey. There are also reports of cannibalism among wild tiger snakes. Prey items are quickly captured and subdued by the powerful poison, sometimes constricting it.
Adult snakes are known to use constriction of large prey. They are important predators of introduced rodents and willingly enter the burrows of mice, rats and even rabbits in search of their prey. On a number of offshore islands, young tiger snakes feed on small lizards, then, as they approach maturity, the diet switches to gray petrel chicks. Because these resources are limited, competition is fierce and there is less than a one percent chance these snakes will reach maturity. They will occasionally eat carrion.
Character and lifestyle features
Tiger snakes become inactive during the winter, retreating into rodent burrows, hollow logs and tree stumps, under large boulders and can crawl up to 1.2 m underground. However, they can also be found basking in the sun on warm winter days. Groups of 26 young snakes are often found in the same place, but they stay there for no more than 15 days, after which they crawl away to another place, with males more prone to wandering.
The snake's large size, aggressive defensive behavior, and highly venomous venom make it extremely dangerous to humans. Although generally calm and avoiding conflict, the cornered tiger snake displays a threat by holding the front of the face in a tense, free curve, with its head slightly raised towards the perpetrator. It will hiss loudly as it inflates and deflates its body, and if provoked further, it will lash out and bite hard.
Interesting fact: Highly toxic poison is produced in large quantities. It affects the central nervous system, but also causes muscle damage and affects blood clotting. The breakdown of muscle tissue can lead to kidney failure.
Tiger snake venom is highly neurotoxic and coagulant, and anyone bitten by a tiger snake should seek immediate medical attention. Between 2005 and 2015, tiger snakes accounted for 17% of identified snakebite victims in Australia, with four reported deaths out of 119 bitten victims. Symptoms of a bite include localized foot and neck pain, tingling, numbness, and sweating, followed by breathing problems and paralysis fairly quickly.
Social Structure and Reproduction
Males can be mature at 500g and females — with a mass of at least 325 g. At the beginning of the breeding season, the males enter into battle, in which each of the two applicants tries to press each other with his head, and as a result, the bodies of the snakes are intertwined. Sexual activity in these reptiles is sporadic throughout the summer and peaks in late January and February. Mating can last up to 7 hours, the female sometimes drags the male. Males do not eat during periods of sexual activity. Females stop eating 3-4 weeks before giving birth.
Interesting fact: These are viviparous animals. Female brood sizes have been recorded up to 126 juveniles. But basically it is 20 — 60 live cubs. The number of babies is often related to the size of the female body.
Tiger snakes from small islands are smaller and produce smaller offspring. The length of the young tiger snake is 215 — 270 mm. Females give birth to cubs at best every second year. There is no maternal care among tiger snakes. They don't become more aggressive during the breeding season, but a male snake keeping an eye on a female may well focus on other things.
Mating at the end of the season is beneficial for the southern species, it gives them the opportunity to start breeding before spring. On the main island of Tasmania, mating has been observed lasting up to seven hours. Mighty females can be relatively sedentary, with one heavy female in Tasmania remaining in her “home” for 50 days. In southwestern Australia, females give birth between late summer and mid-autumn (March 17 — May 18).
Tiger snake natural enemies
When threatened, tiger snakes spread their bodies and raise their heads off the ground in a classic pre-strike pose. When threatened, the neck and upper body can be greatly flattened, revealing black skin between relatively large, semi-glossy scales. Known predators of tiger snakes include: Cryptophis nigrescens (a species of endemic venomous snake) and some birds of prey such as shrikes, hawks, birds of prey, ibises and kookaburras.
Interesting fact: In one study conducted on the island of Karnak, most of the tiger snakes were blind in one eye in 6.7% of cases, and in both eyes in 7.0%. This was due to attacks by nesting gulls. While not predation per se, it increases the catch of snakes by hunters of rare animals and therefore increases the likelihood of them being taken by other predators.
Tiger snakes have also been subjected to severe persecution by people in the past and still regularly die in a collision. Many also become victims of cars on the road. The tiger snake uses venom to destroy its prey and may bite the aggressor. It is a slow and cautious hunter that can stand still, relying on its imposing menacing posture for protection.
Like most snakes, tiger snakes are shy at first and then bluff and attack as a last resort. When threatened, the tiger snake will spread its neck, raising its head to look as intimidating as possible. If the threat persists, the snake will often feign a strike by producing an explosive hiss or “bark” at the same time. Like most snakes, tiger snakes will not bite unless provoked.
Population and species status
Snakes are known for their stealth and, as a result, few natural populations have been accurately described in the long term. Monitoring of the population of tiger snakes (scutatus) was carried out on Karnak Island. This is a small limestone island (16 hectares) off the coast of Western Australia. Population estimates show that snake density is very high, over 20 adult snakes per hectare.
This high predator density may be explained by the fact that adult snakes feed mainly on nestlings of nesting birds that breed in large colonies on Karnak and forage elsewhere. The annual growth rate of body size in most individuals indicates the high availability of food on the island. Sex ratios vary greatly, with males greatly outnumbering females.
Interesting fact: Biomass growth rates declined more sharply in adult females than males, while annual body weight changes were similar both sexes probably. Perhaps this was due to the high energy costs of reproduction experienced by females.
The Flinders Range subpopulation is threatened by overgrazing, habitat clearing, soil erosion, water pollution, fires, and food loss. This subpopulation is found in Mount Wonderful National Park, South Australia.
Tiger Snake Conservation
Large-scale development of wetlands in the coastal plains of Western Australia is significantly reducing the population of this species. The subpopulations on the Garden and Karnak Islands are safe due to their isolated location. Populations in the Sydney region have declined, presumably due to loss of habitat and food. Potential predators include cats, foxes and dogs, which has an impact on the number of tiger snakes.
Interesting fact: In all Australian states, tiger snakes are a protected species, and for killing or causing harm, you can get a fine of up to $ 7,500, and in some states imprisonment for up to 18 months. It is also illegal to export the Australian snake.
The subpopulation, sometimes recognized as a separate subspecies of Notechis scutatus serventyi on Chappell Island, has a limited range and is listed by the IUCN as vulnerable in Tasmania. The Friedes Ridge (Notechis ater ater ) population is also listed as Vulnerable (Commonwealth, IUCN).
Invasion of cane venom toads could affect this species, as frogs are an important part of the snake's diet. Further research into the impacts of this species is needed, however, it is mainly a southern temperate snake and is unlikely to substantially coincide with the potential distribution of the cane toad. The tiger snake is an important link in the animal world of Australia, some species of which need the help of international organizations to save their populations.