Giant monitor

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Giant monitor
Giant monitor (Varanus giganteus)

Giant monitor ( Varanus giganteus )

Systematics
without rank: Toxicofera
without rank: Sneaky (Anguimorpha)
Family : Varanidae
Genre : Monitor lizards ( varanus )
Subgenus : Varanus
Type : Giant monitor
Scientific name
Varanus giganteus
( Gray , 1845)

The giant monitor lizard ( Varanus giganteus ) is a species of monitor lizard ( Varanus ) native to Australia . As the largest lizard in Australia, it reaches lengths of over 2 m in exceptional cases and can be easily distinguished from other monitor lizards by a black net pattern on the head, throat and neck as well as a brown back color with light spots. It lives in particular in arid areas with rock formations.

Like all monitor lizards, the giant monitor is a diurnal loner and spends the night in a hiding place. Its diet consists mainly of lizards, other small vertebrates and insects as well as carrion. During the dry season (Australian winter) the animals hide in their burrows for weeks, the rest period is followed by the breeding season in spring and summer.

features

Giant monitor in a Sydney zoo

The giant monitor is the largest monitor in Australia, in very rare cases it reaches a total length of 2–2.5 m. Usually, however, the species remains smaller and rarely grows more than 2 m long. Males are significantly larger than females; at sexually mature males are on average 23% longer and weigh 2.5 times as much as females ( sexual dimorphism ). In a field study in Western Australia, males averaged 149.4 cm in length and females averaged 130.3 cm.

Despite its size, the giant monitor is quite slim. The nostrils of this species are round to oval, lie on the side of the head and are very close to the tip of the snout. The fingers have strong, sharp claws. The tail is usually less than 1.5 times as long as the head and trunk and therefore relatively short. The tail is strongly flattened laterally.

The scales on the head and neck are very small and smooth. The scales of the trunk are also smooth and arranged in 150–155 transverse rows from the throat fold to the base of the hind legs. The scales on the tail are keeled.

The top of the body is dark brown to black. On the upper side of the body there are large, black-edged, yellow spots. They are arranged in transverse rows and can be found from the neck up to 2/3 the length of the tail. In addition to these large, distinctive spots, adult specimens usually have numerous small, yellow spots. The last third of the tail shows only yellowish-white spots on the underside. The underside of the body is whitish and there is a pronounced reticulation on the throat.

The tracks of the giant monitor can be distinguished from many other monitors by their size. The dragging track of the tail is much narrower than that of the black monitor ( V. tristis ), and in the case of the giant monitor it is occasionally interrupted. The back foot is placed directly behind or on the imprints of the front foot. A species differentiation based on monitor tracks is only possible to a very limited extent.

distribution and habitat

Distribution of the giant monitor - dots stand for reliable evidence, orange for probable distribution.

The giant monitor lives in the arid regions of Australia - its range extends from the central west coast to the east to central Queensland . Giant monitors are most commonly found in rocky areas, but also live in sandy deserts, rockless forest and scrubland and in Spinifex grassland.

Way of life

activity

The giant monitor is predominantly ground dwelling. Like all monitor lizards, the species is diurnal; at night the animals hide in self-dug burrows in the ground, in buildings made by other animals or in crevices. During the rainy season, the activity pattern is bimodal: in the early morning the lizards sunbathe to reach their activity temperature. At lunchtime, giant monitors hide in their constructions to avoid overheating; For this purpose, they dig up to 8 m long and 1 m deep caves in the Great Victoria Desert . After the activity peak in the early morning, there is another activity peak in the late afternoon.

During the dry season with little food, giant monitors often remain inactive in their burrows for several weeks or months, during which time they probably feed on fat reserves. Giant monitors are only rarely active during this time of year, in such cases the activity is limited to the warm enough lunchtime.

Giant monitors show extensive thermoregulatory behavior, which manifests itself in the active search for places in the sun, the retreat into colder microclimate and the alignment of the body to the sun depending on the temperature requirement. In active individuals, the average body temperature is around 35–37 ° C.

Social behavior and spaces for action

Like all monitor lizards, the giant monitor is a loner. Typical war commentary fights are described for the giant monitor, with which disputes over reproductive partners, food, hiding places or sun places are resolved. In the mating season in particular, injuries from bites and scratches apparently occur occasionally.

Giant monitors are not territorial, but move in an ancestral area that can be described as an area of action . These areas are retained for years and overlap with the action spaces of other individuals. In a study on the North West Cape , females had an area of ​​action averaging 64.8 hectares, those of males were on average 240.1 hectares. During the mating season, the males greatly expand their range of action to search for females. Often the size of the action area doubles, in one single case a male moved in an area of ​​1156.8 ha.

nutrition

The giant monitor is a carnivore and feeds on a variety of prey as well as carrion. Lizards make up about half of the diet. While most lizard-eating monitor lizards hunt geckos or skinks , the giant monitor lizard prefers agamas . In addition, mainly insects and small mammals are eaten. Overall, larger vertebrates appear to be significantly more important than invertebrates. This is in contrast to many other, mostly insectivorous monitor lizards. Occasionally giant monitor lizards also attack very large mammals such as small kangaroos; As many of these native prey have become very rare in some areas, giant monitors are increasingly hunting the recently introduced hares. The carrion eaten by giant monitor lizards often comes from " roadkills ", ie animals that perished in traffic. On Barrow Island (Western Australia) , sea ​​turtle eggs are seasonally very important prey.

Like most monitor lizards, the giant monitor searches large areas for prey. Giant monitors have also been observed lurking under cars for seagulls , which are then attacked in a sprint.

Occasionally, giant monitors prey on unusually large prey. There is also a report that a 1.5 m long giant monitor completely devoured a 1.2 m long conspecific.

Reproduction and development

While there are extensive reports on reproduction in captivity, little is known about reproduction in the wild. The females reach sexual maturity with a head-trunk length of 49 cm, the males with 45 cm. The mating season falls in late spring and early summer, and eggs are laid in early to mid-summer. The males, flickering, look for the females, who release pheromones . In some cases, the males are obviously familiar with the hiding places the females have kept for years and sometimes seek them out specifically to mate.

The gestation period lasts around 4 weeks in captivity, the eggs are laid in captivity in self-dug earth nests. The clutches contain 5–13 eggs in captivity. In the wild, the incubation lasts 11–12 months, so the young hatch in the spring or early summer of the following year. When hatched, the young measure 19.2–22.7 cm head-trunk length, 49.75–59.1 cm overall length and weigh 63–96 g. In nature, yearlings grow to a head-trunk length of about 30 cm, after 2 years they reach 40 cm head-trunk length, and after 3 years 45 cm head-trunk length.

Natural enemies, enemy avoidance and life expectancy

While adult giant monitors have only a few enemies, there is a high mortality rate, especially among young specimens. Predators include birds of prey, snakes, other monitor lizards, cats, foxes and dingoes . The animals flee from enemies and humans in trees, in hiding places and in rare cases also in the water. The giant monitor is considered to be comparatively shy, even if large specimens do not necessarily flee when approaching slowly. If they are frightened, giant monitors are very agile and can e.g. B. drop 6 m deep or stand up on your hind legs and run on two legs.

Among the most important parasites of Riesenwarans belonging nematode ABBREVIATA perenticola which very specifically affects the Perentie.

There is no information on the life expectancy of giant monitor lizards living in the wild; in captivity, the species can live to be over 20 years.

Systematics

V. giganteus was first described by John Edward Gray in 1845 . He described the species in the Catalog of the specimens of lizards in the collection of the British Museum and referred to a Barrow Island specimen in the Natural History Museum , which he then called Hydrosaurus giganteus . In 1885 George Albert Boulenger placed the species in the genus Varanus . On the basis of its hemipenis morphology , V. giganteus is placed in the subgenus Varanus . According to investigations by mtDNA , Fitch and colleagues (2006) placed V. giganteus in the Indo-Australian cladus, where V. giganteus is assigned to the V. gouldii group. According to the analyzes by Fitch and colleagues (2006), the closest relatives of V. giganteus are the species V. mertensi and V. spenceri , these three species form a monophylum in any interpretation of the mtDNA data .

No subspecies of the giant monitor are recognized.

Cultural references

The giant monitor is traditionally hunted by Aborigines . The Aborigines know a number of legends about the giant monitor. It is often said that the giant monitor and the black monitor ( V. tristis ) got their coloring by painting on each other. The giant monitor is said to have made a great effort, which is said to have given the mourning monitor its fine rosette markings. In return, the mourning monitor got tired during its work and poured its paint bucket over the back of the giant monitor, which is said to have resulted in its rather monotonous coloration. As a punishment, the giant monitor had forced the much smaller weeping monitor to live in the trees; In fact, the black monkey lives in trees and is occasionally hunted by the giant monitor.

In Australia the giant monitor is called Perentie , this name comes from an Aboriginal language.

Danger

The giant monitor is listed in Appendix II of the Washington Convention on Species Protection . Because of its wide distribution, it is not considered endangered, but the populations can be decimated by neozoa such as feral dogs, cats and red foxes.

Web links

Commons : Varanus giganteus  - collection of images, videos and audio files

literature

  • NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus: A Field Study of Australia's Largest Monitor Lizard. In: Hans-Georg Horn, Wolfgang Böhme, Uwe Krebs: Advances in Monitor Research. III (= Mertensiella. 16). 2007, ISBN 978-3-9806577-9-2 , pp. 255-290.
  • HG Horn, DR King: Varanus giganteus. In: ER Pianka, DR King (Ed.): Varanoid Lizards of the World. Indiana University Press, Bloomington & Indianapolis 2004, ISBN 0-253-34366-6 , pp. 335-354.
  • DR King, B. Green, H. Butler: The Activity Pattern, Temperature Regulation and Diet of Varanus giganteus on Barrow Island, Western Australia. In: Australian Wildlife Research. 16 (1), 1989, pp. 41-47.

supporting documents

  1. ^ HG Horn, DR King: Varanus giganteus. 2004, p. 340.
  2. ^ NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus. 2007, p. 267.
  3. ^ NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus. 2007, p. 266.
  4. ↑ a b HG Horn, DR King: Varanus giganteus. 2004, p. 338.
  5. ^ HG Horn, DR King: Varanus giganteus. 2004, pp. 338-340.
  6. ^ JO Farlow, ER Pianka: Body Form and Trackway Pattern in Australian Desert Monitors (Squamata: Varanidae): Comparing Zoological and Ichnological Diversity. In: Palaios. 15 (3), 2000, pp. 235-247.
  7. ^ HG Horn, DR King: Varanus giganteus. 2004, p. 337.
  8. ^ A b SA Thompson, PC Withers, GG Thompson, D. Robinson: Range extension for the Perentie, Varanus giganteus (Squamata: Varanidae). In: Journal of the Royal Society of Western Australia. 88, 2005, pp. 41-43.
  9. ^ A b c d ER Pianka: Comparative Ecology of Varanus in the Great Victoria Desert. In: Australian Journal of Ecology. 19, 1994, pp. 395-408.
  10. ↑ a b c Varanus giganteus (GRAY 1845). In: D. Bennett: Monitor lizards of the world. World of monitor lizards. Edition Chimaira, Frankfurt am Main 1996, ISBN 3-930612-05-4 , pp. 173-177.
  11. ^ HG Horn, DR King: Varanus giganteus. 2004, p. 341.
  12. ^ HG Horn, DR King: Varanus giganteus. 2004, p. 342.
  13. ^ NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus. 2007, p. 274.
  14. ↑ a b c NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus. 2007, p. 275.
  15. ↑ a b HG Horn, DR King: Varanus giganteus. 2004, p. 347.
  16. ^ NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus. 2007, p. 280.
  17. ^ HG Horn, DR King: Varanus giganteus. 2004, p. 345.
  18. ^ HG Horn, DR King: Varanus giganteus. 2004, pp. 344-345.
  19. ^ A b NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus. 2007, p. 283.
  20. ^ NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus. 2007, pp. 276-277.
  21. ↑ a b c HG Horn, DR King: Varanus giganteus. 2004, pp. 343-344.
  22. ↑ a b CD James, JB Losos, DR King: Reproductive Biology and Diets of Goannas (Reptilia: Varanidae) from Australia. In: Journal of Herpetology. 26 (2), 1992, pp. 128-136.
  23. ^ S. MacDonald: Observations on the Stomach Contents of a Road-killed Perentie, Varanus giganteus in Western Queensland. In: Biawak. 1 (1), 2007, pp. 21-23.
  24. ↑ JB Losos, HW Greene: Ecological and evolutionary implications of diet in monitor lizards. In: Biological Journal of the Linnean Society. 35 (4), 1988, pp. 379-407.
  25. ↑ a b DR King, B. Green, H. Butler: The Activity Pattern, Temperature Regulation and Diet of Varanus giganteus. 1989, p. 45.
  26. ↑ a b c HG Horn, DR King: Varanus giganteus. 2004, p. 343.
  27. ^ S. Wilson, G. Swan: A complete guide to reptiles of Australia. 3. Edition. New Holland Publishers, Sydney / Auckland / London / Cape Town 2010, ISBN 978-1-877069-76-5 , p. 394.
  28. ^ HG Horn, DR King: Varanus giganteus. 2004, p. 350.
  29. ^ NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus. 2007, pp. 265-266.
  30. ^ NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus. 2007, p. 282.
  31. ^ HG Horn, DR King: Varanus giganteus. 2004, p. 351.
  32. ^ A b NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus. 2007, p. 284.
  33. ^ NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus. 2007, p. 269.
  34. ^ HG Horn, DR King: Varanus giganteus. 2004, p. 344.
  35. ^ HG Horn, DR King: Varanus giganteus. 2004, p. 353.
  36. ^ JE Gray: Catalog of the specimens of lizards in the collection of the British Museum. Trustees of the British Museum. Edward Newman, London 1845.
  37. ^ GA Boulenger: Catalog of the lizards in the British Museum (Natural History). Vol. 2, 2nd edition. London 1885.
  38. ↑ a b W. Böhme: Checklist of the living monitor lizards of the world (family Varanidae). In: Zoologische Verhandelingen. 341, 2003, pp. 3-43.
  39. ↑ AJ Fitch, AE Goodman, SC Donnellan: A molecular phylogeny of the Australian monitor lizards (Squamata: Varanidae) inferred from mitochondrial DNA sequences. In: Australian Journal of Zoology. 54, 2006, pp. 253-269.
  40. ↑ ER Pianka: The Lizard Man Speaks. University of Texas Press, 1994, ISBN 0-292-76552-5 , p. 137.
  41. ^ NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus. 2007, p. 257.
  42. ^ HG Horn, DR King: Varanus giganteus. 2004, p. 354.

Remarks

  1. ^ In NA Heger, TG Heger: Behavior, Ecology and Thermal Physiology of Varanus giganteus. 2007, p. 283 speaks of “ breeding does take place from late spring (December) to early summer (January) and nesting takes place in early to mid spring (January and February) ” . The nesting time in the “ spring ” is obviously a mistake, as the nesting time according to the month is in the early to mid-summer. This error has been corrected in the article.