Mitchell's water monitor

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Mitchell's water monitor
Varanus mitchelli.jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Family: Varanidae
Genus: Varanus
Subgenus: Odatria
Species:
V. mitchelli
Binomial name
Varanus mitchelli
Mertens, 1958 [2] [3]

Mitchell's water monitor (Varanus mitchelli) is a semiaquatic species of monitor lizard in the family Varanidae. The species is native to Australia. [4] The species is native to the Northern regions of Australia, and is on IUCN's Red List as a critically endangered species. They can be distinguished by the orange or yellow stripes along their neck and dark spots along their back. They are mainly carnivorous, and eat small prey such as lizard, birds, and insects.

Contents

Etymology

The specific name, mitchelli, as well as the common name, Mitchell's water monitor, are in honor of Australian herpetologist Francis John Mitchell (1929–1970) of the South Australian Museum. [5] [6] The classification Varanus is a Latinization of the Arabic word for monitor lizard, waran. [7] The Mitchell's Water Monitor, as well as other species of Monitors in Australia, are colloquially referred to as goannas in Australia. The name likely came from the word iguana, as the lizards looked like the iguanas of South America to the first European settlers of Australia.

Description

Varanus mitchelli reaches a length of up to 70 cm (28 in). It has a long, slender neck and a pointed head. It is generally dark brown or black and has small yellow and white spots covering the limbs and head, and ocelli with dark centers as well as yellow stripes along its side. [8] [2] The skin is rough, with many wrinkles. Its underside is a light cream color. [8]

Varanus lizards, including V. mitchelli have excellent eyesight, but are "night blind" in the dark. [9] The lizards' retinas do not have rods, the receptor cells for night vision.

The Mitchell's Water Monitor has yellow and orange stripes down its sides and neck. Mitchell's Water Monitor.jpg
The Mitchell's Water Monitor has yellow and orange stripes down its sides and neck.

Geographic range

Mitchell's water monitor resides along all northern river systems in the Kimberly Region of Western Australia and the Northern Territory. [8] [2] [3] There is no data to suggest that they live on any islands surrounding Australia. [8]

Habitat

V. mitchelli inhabit swamps, lagoons, inland rivers, and other bodies of water and are often found on trees near the water. It prefers to climb trees to shelter in tree hollows or under bark. [4] [5] If disturbed, V. mitchelli will head to the water. [4] V. mitchelli frequently basks on rocks near the water. [6]

The geographic range of the Mitchell's Water Monitor. Mitchell's Water Monitor distribution.tiff
The geographic range of the Mitchell's Water Monitor.

Reproduction

Varanus mitchelli is oviparous. [10] V. Mitchelli breed during the dry season, with the females laying eggs between April and June. [11] Clutch sizes have been recorded from 3 to 12. Breeding behaviors are found to be similar to other species of Varanus lizards. [11] They live around 10 years. [12]

In captivity

The Mitchell's water monitor is reported to be nervous and shy. It is rarely kept in captivity. [13] Average clutch sizes for V. mitchelli are between 3-11 eggs, though they can lay up to 20 in captivity. [14] They are found to be easily bred in captivity.

[14]

This lizard grows to a over 2 ft in length and requires a large bioactive enclosure, recommendations of 8x4x4 ft are not uncommon, especially if attempting to breed. Providing a seasonal environment and food to mimic natural behaviors is the best onset for breeding although these requirements can be difficult to achieve and reduces their appearance in captivity.

Diet

Mitchell's water monitor preys on smaller animals of both terrestrial and aquatic origin. Its prey includes: smaller lizards, small mammals, nestling birds, reptile eggs and terrestrial invertebrates (orthopterans, arachnids, beetles etc.). Aquatic prey include: fish, crabs and frogs. [15] Its diet changes seasonally according to flooding during the wet season. [16]

Conservation

Threats

The current most significant threat to the Mitchell's Water Monitor is the spread of Cane Toads across the Northern Territory in Australia. [17] Toads and frogs are a part of V. Mitchelli's diet, though the Cane Toads are poisonous to many species of Water Monitors, including V. Mitchelli. [17] Cane Toads have become an invasive species in Australia since their introduction to the area in 1935, and Australia is currently facing an overpopulation of Cane Toads, which presents a problem for the species who mistake the poisonous Cane Toads for endemic toads native to Australia that make up the lizards' usual diet. [18] The geographic range of the cane toads completely overlaps the geographic range of V. mitchelli. [8] Not all cane toads are entirely lethal: the smaller ones have non-lethal doses of poison compared to the larger toads, however, the Mitchell's Water Monitor and other monitors will go after the larger toads that contain lethal doses.

Other threats to the Mitchell's Water Monitor include habitat loss due to land clearing, habitat degradation and change due to climate change, and deaths occurring from contact with humans, such as death on roads. [7] V. mitchelli have also been reported to be exported live to be sold in global markets. [19]

Status

Mitchell's Water Monitor is currently classified as critically endangered according to IUCN's Red List. [12] Its population is decreasing. [12] The decrease of V. mitchelli following the introduction of the Cane Toads has been estimated to be as high as 97% after only three years. [20] At Kakadu National park, almost the entire population of Mitchell's Water Monitor was taken out by the arrival of the cane toads, though a 2020 survey of the area found some individuals of the species. [21] Despite this, the species has persisted at many habitat spots, though as sightings are rare there is no current estimate on the number of individuals in each population of V. mitchelli. [8]

Efforts

Researches are trying to find ways to make monitor lizards avoid the cane toads. One current strategy is called Conditioned Taste Aversion Therapy, or CTA. This is where the animal associates a certain food with illness. The animal will avoid this food in the future because of the association. Researchers at the University of Sydney offered small cane toads with a non-lethal amount of poison to monitors in an area where the toads haven't reached yet, and found that the monitors who ate the small toads avoided them in the future. [22] These small toads, or "teacher toads" only make the lizards sick, but it is enough to dissuade them from eating the toads again. Other reports of successful CTA include the use of non-living bait. [23] In order for this prevention strategy to work, scientists would have to identify areas of concentrated biodiversity in order for the results to balance out the cost of the bait. [23] As cane toads march across Australia, scientists believe that releasing smaller toads ahead of the larger ones will increase CTA in lizards, and prevent them from eating the toads that contain a lethal amount of poison.

Other efforts are aimed at protecting the current populations of Mitchell's Water Monitor at sites already occupied by cane toads, as it will be extremely difficult to stop the spread of cane toads. [8]

The Northern Territory Government has set up the Island Arks program to help the conservation of species affected by the cane toads. [24]

Related Research Articles

<span class="mw-page-title-main">Monitor lizard</span> Genus of reptiles

Monitor lizards are lizards in the genus Varanus, the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the Americas as an invasive species. About 80 species are recognized.

<span class="mw-page-title-main">Nile monitor</span> Species of lizard

The Nile monitor is a large member of the monitor family (Varanidae) found throughout most of Sub-Saharan Africa, particularly in drier regions, and along the Nile River and its tributaries in East Africa. Additionally, there are modern, invasive populations in North America. The population found in West African forests and savannahs is sometimes recognized as a separate species, the West African Nile monitor. While it is dwarfed by its larger relatives, such as the Komodo dragon, the Asian water monitor or the crocodile monitor, it is still one of the largest lizards in the world, reaching Australia’s perentie in size. Other common names include the African small-grain lizard, as well as iguana and various forms derived from it, such as guana, water leguaan or river leguaan.

<span class="mw-page-title-main">Sand goanna</span> Species of lizard

The sand goanna, also known commonly as Gould's monitor, the racehorse goanna, and the sand monitor, is a species of large Australian monitor lizard in the family Varanidae.

<span class="mw-page-title-main">Mangrove monitor</span> Species of lizard

The mangrove monitor, mangrove goanna, or Western Pacific monitor lizard is a member of the monitor lizard family with a large distribution from northern Australia and New Guinea to the Moluccas and Solomon Islands. It grows to lengths of 3.5 to 4 ft. It is also known as wbl yb in the Kalam language of Papua New Guinea.

<span class="mw-page-title-main">Yellow-spotted monitor</span> Species of reptile

The yellow-spotted monitor, also known as the Argus monitor, is a monitor lizard found in northern and western regions of Australia and southern New Guinea.

<span class="mw-page-title-main">Spiny-tailed monitor</span> Species of lizard

The spiny-tailed monitor, also known as the Australian spiny-tailed monitor, the ridge-tailed monitor the Ackie dwarf monitor, and colloquially simply ackie monitor, is an Australian species of lizard belonging to the genus of monitor lizards (Varanus).

<span class="mw-page-title-main">Mertens' water monitor</span> Species of lizard

Mertens' water monitor, often misspelled Mertin's water monitor, is a species of monitor lizard. The species is endemic to northern Australia, and is a wide-ranging, actively foraging, opportunistic predator of aquatic and riparian habitats. It is named after German herpetologist Robert Mertens.

<span class="mw-page-title-main">Pygmy mulga monitor</span> Species of lizard

The pygmy mulga monitor, also known commonly as Gillen's monitor or just the mulga monitor, is a species of lizard in the family Varanidae. The species is endemic to Australia.

<span class="mw-page-title-main">Kimberley rock monitor</span> Species of lizard

The Kimberley rock monitor is a medium-sized species of monitor lizard in the family Varanidae. The species is native to Northern Australia. Also known commonly as Glauert's monitor and the Kakadu sand goanna, it belongs to the subgenus Odatria.

<span class="mw-page-title-main">Rosenberg's monitor</span> Species of lizard

The Rosenberg's monitor is an Australian species of varanid reptile found in southern regions of the continent. They are large and fast predators with rugged bodies and long tails, having a combined length up to 1.5 metres, that will consume any smaller animal that is pursued and captured or found while foraging. They occur in the Australian Capital Territory, New South Wales, South Australia, Victoria, where it may be rare or locally common, and more frequently observed in Western Australia, where it is sometimes abundant.

The black-spotted ridge-tailed monitor, also called commonly the black-spotted spiny-tailed monitor, the lemon-throated monitor, the northern ridge-tailed monitor, Whites monitor, and the yellow-throated monitor, is a subspecies of lizard in the family Varanidae. The subspecies is native to Australia's tropical Northern Territory. It is listed as Least Concern on the IUCN Red List as it is considered common and not threatened. It was first described in 1987. It is also known as White's dwarf goanna.

<span class="mw-page-title-main">Blue-tailed monitor</span> Species of lizard

The blue-tailed monitor, blue-tailed tree monitor or Kalabeck's monitor, is a monitor lizard of the Varanidae family. It belongs to the V. doreanus group of the subgenus Euprepiosaurus.

<span class="mw-page-title-main">Dumeril's monitor</span> Species of lizard

Dumeril's monitor is a species of lizard in the family Varanidae. The species is endemic to Southeast Asia.

<span class="mw-page-title-main">Black-palmed rock monitor</span> Species of lizard

The black-palmed rock monitor is a member of the Varanidae family found in Australia. Also known as the twilight monitor or the long-tailed rock monitor, it is a member of the subgenus Odatria, and is found in the northern part of Australia in the Northern Territory and Western Australia, as well as Queensland. Specifically, its distribution extends from Mount Isa in the east to the Kimberleys in the west. Its habitat is areas of rock escarpment, and large populations may be found in small areas.

Varanus keithhornei, commonly known as the canopy goanna, Keith Horne's monitor, blue-nosed tree monitor, or Nesbit River monitor, is a species of monitor lizards native to northeast Australia. It is a member of the Varanus prasinus species group.

<span class="mw-page-title-main">Kings' monitor</span> Species of lizard

Kings' monitor, also known commonly as Kings' goanna, Kings' rock monitor and pygmy rock monitor, is a small species of monitor lizard in the family Varanidae. The species is native to Australia.

<span class="mw-page-title-main">Marbled water monitor</span> Species of lizard

The marbled water monitor, also known commonly as the Philippine water monitor, is a large species of monitor lizard in the family Varanidae. The species is endemic to the Philippines.

<i>Varanus spinulosus</i> Species of lizard

Varanus spinulosus, the Solomon Island spiny monitor, Isabel monitor, or spiny-neck monitor, is a species of monitor lizard. It is endemic to the Solomon Islands archipelago and is also known from Santa Isabel Island, San Jorge Island and Bourgainville Island.

<i>Varanus storri</i> Species of lizard

Storr's monitor is a species of monitor lizard in the family Varanidae. The species is endemic to Australia.

<i>Varanus <span style="font-style:normal;">(</span>Odatria<span style="font-style:normal;">)</span></i> Subgenus of reptiles

Odatria, commonly known as dwarf monitors, consists of small monitor lizards found in Australia and Indonesia. Species in this subgenus include the smallest monitor species in the world, the tiny 16 gram Dampier Peninsula monitor, but also includes some more medium sized species such as the 240 gram black-palmed rock monitor.

References

  1. ↑ Shea, G.; Woinarski, J.C.Z.; Cogger, H. (2018). "Varanus mitchelli". IUCN Red List of Threatened Species . 2018: e.T83778268A101752345. doi: 10.2305/IUCN.UK.2018-1.RLTS.T83778268A101752345.en . Retrieved 18 November 2021.
  2. 1 2 3 Goannas (lizard family Varanidae). Komododragon.biz. Retrieved on 2012-08-22.
  3. 1 2 "GBIF.org" . Retrieved 3 July 2010.
  4. 1 2 3 Böhme, Wolfgang [in German] (2003), Checklist of the living lizards of the world (family Varanidae), Nationaal Natuurhistorisch Museum, p. 32, ISBN   978-90-73239-86-9
  5. 1 2 Pianka, Eric R.; King, Dennis; King, Ruth Allen (2004). Varanoid lizards of the world. Indiana University Press. ISBN   978-0-253-34366-6 . Retrieved 2010-07-04.
  6. 1 2 Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). The Eponym Dictionary of Reptiles. Baltimore: Johns Hopkins University Press. xiii + 296 pp. ISBN   978-1-4214-0135-5. (Varanus mitchelli, p. 179).
  7. 1 2 Macdonald, Stewart (2007). "Mitchell's Water Monitor". AROD.guide. Retrieved October 17, 2022.
  8. 1 2 3 4 5 6 7 Australia Department of Environment, Parks and Water Security, Threatened species of the Northern Territory, November 2021.
  9. ↑ Jackson, Timothy (2020-05-28). "Are monitor lizards venomous? (the Tale of Toxicofera, part 4)". School of Biomedical Sciences. Retrieved 2022-10-16.
  10. ↑ Species Varanus mitchelli at The Reptile Database . www.reptile-database.org.
  11. 1 2 Gaikhorst, Glen; McLaughlin, James; Larkin, Brian; McPharlin, Meagan (18 May 2009). "Successful captive breeding of Mitchell's water monitor, Varanus mitchelli (Mertens 1958), at Perth Zoo". Zoo Biology. 29 (5): 615–625. doi:10.1002/zoo.20244. PMID   19459149.
  12. 1 2 3 Shea, G., Woinarski, J. & Cogger, H. 2018. Varanus mitchelli. The IUCN Red List of Threatened Species 2018: e.T83778268A101752345. doi : 10.2305/IUCN.UK.2018-1.RLTS.T83778268A101752345.en. Accessed on 26 September 2022.
  13. ↑ Gaikhorst, Glen; McLaughlin, James; Larkin, Brian; McPharlin, Meagan (18 May 2009). "Successful captive breeding of Mitchell's water monitor, Varanus mitchelli (Mertens 1958), at Perth Zoo". Zoo Biology. 29 (5): 615–625. doi:10.1002/zoo.20244. PMID   19459149.
  14. 1 2 Gaikhorst, Glen; McLaughlin, James; Larkin, Brian; McPharlin, Meagan (18 May 2009). "Successful captive breeding of Mitchell's water monitor, Varanus mitchelli (Mertens 1958), at Perth Zoo". Zoo Biology. 29 (5): 615–625. doi:10.1002/zoo.20244. PMID   19459149.
  15. ↑ "Mampam.com" . Retrieved 3 July 2010.
  16. ↑ Gaikhorst, Glen; McLaughlin, James; Larkin, Brian; McPharlin, Meagan (18 May 2009). "Successful captive breeding of Mitchell's water monitor, Varanus mitchelli (Mertens 1958), at Perth Zoo". Zoo Biology. 29 (5): 615–625. doi:10.1002/zoo.20244. PMID   19459149.
  17. 1 2 Doody, J. Sean; Soanes, Rebekah; Castellano, Christina M.; Rhind, David; Green, Brian; McHenry, Colin R.; Clulow, Simon (September 1, 2015). "Invasive toads shift predator–prey densities in animal communities by removing top predators". Ecology. 96 (9): 2544–2554. doi: 10.1890/14-1332.1 . ISSN   0012-9658. PMID   26594710.
  18. ↑ Lower, Brian H.; Shaul, Travis R.; Shaul, Kylienne A.; Weaver, and Ella M. "Cane Toad: Purposefully Introduced, but Instantly a Regret". Environmental ScienceBites.
  19. ↑ Biawak. "Monitoring the Trade: Using the CITES Database to Examine the Global Trade in Live Monitor Lizards (Varanus spp.)" 3(2), pp. 37-45 © 2009 by International Varanid Interest Group
  20. ↑ Doody, J.S., Green, B., Rhind, D., Castellano, C.M., Sims, R. and Robinson, T. 2009. Population-level declines in Australian predators caused by an invasive species. Animal Conservation 12: 46-53.
  21. ↑ Einoder LD, Gillespie GR and Buckley KA (2020) Terrestrial fauna monitoring in Kakadu National Park. Northern Territory Department of Environment, Parks and Water Security, Darwin.
  22. ↑ "Researchers stop threatened lizards eating toxic cane toads". The University of Sydney. Retrieved 2022-10-16.
  23. 1 2 Aiyer, Abhilasha; Bunuba Rangers; Bell, Tina; Shine, Richard; Somaweera, Ruchira; Bruny, Miles; Ward-Fear, Georgia (June 2, 2022). "Taking the bait: Developing a bait delivery system to target free-ranging crocodiles and varanid lizards with a novel conservation strategy". Ecology and Evolution. 12 (6): e8933. doi:10.1002/ece3.8933. ISSN   2045-7758. PMC   9163195 . PMID   35784020.
  24. ↑ Hyatt, Alex. "Battlelines drawn against the cane toad march." 2004.

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