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Varanus salvator Print E-mail
Water monitor, Asiatic water monitor

Varanus salvator

Varanus salvator salvator Laurenti 1788
Varanus salvator cummingi  Martin 1838
Varanus salvator nuchalis   Gunther 1872
Varanus salvator marmoratus Weigmenn 1834
Varanus salvator bivittatus Kuhl 1820
Varanus salvator togianus  Peters 1872
Varanus salvator andamanensis Deraniyagala 1944

Varanus salvator
The water monitor is one of the largest and most widespread of  the monitor lizards. It is of greater economic importance than any other varanid and millions are killed each year for their meat and skins. Despite this heavy collecting water monitors are still very common in many areas, although in India numbers have dwindled severely in the last 150 years. Large populations can still be found on the Andamen and Nicobar Islands, and in Sri Lanka, but on the mainland they have survived only in Orissa, west Bengal, Assam, around Calcutta and in the Garo Hills. They may also be present in the eastern Himalayas (Parry 1932; Smith 1935; Whitaker & Whitaker 1980; Whitaker & Khan 1982; Auffenberg 1986; Luxmoore & Groombridge 1990; Das 1989; Pandav 1993). Its disappearance appears to be due to a combination of overcollecting and habitat destruction, especially the clearing of mangrove forests. Similarly, populations in Bangladesh appear to have been decimated in recent years (Khan 1988).

Further south the animals are still plentiful in most areas, with large populations reported in southern China (Yunnan, Kwantung, Kwangshi and Hanain), Burma, Thailand, Laos, Kampuchea, Vietnam, Malaysia, Borneo, the Philippines and the Indonesian Islands as far east as Flores and Sulawesi or Halmahera (Peters & Doria 1878; de Rooij 1915; Schmidt 1927, Smith 1930; Mertens 1942; Nutphand; Harrison & Lim 1957; Auffenberg 1981; Luxmoore & Groombridge 1990; Gaulke 1992; Darevskii pers. comm). Small populations may still exist on islands around Hong Kong (Romer 1963). Their numbers in Kalimantan are said to have declined seriously in recent years, although large populations still exist in many parts of Borneo (Unlam & Untam 1988; Luxmoore & Groombridge 1990). In most parts of the Philippines numbers have greatly declined within living memory (Gaulke 1992b, 1986). In many areas water monitors are extremely numerous; Erdelen (1988, 1991) recorded almost 120kg of water monitor along a 1km stretch of riverbank in Sumatra, one of the highest lizard biomasses recorded anywhere in the world. Munsch (1987) saw seven specimens piled on top of each other on a riverbank. In Bangladesh Khan (1988) estimated densities to be around 7 per km2 in suitable habitats. Water monitor can be found close to the centre of some of south-east Asia's largest cities, but they reach their highest densities in mangrove forests and are never found far from water, be it a ditch or an ocean. Their ability to traverse large bodies of water has allowed them to colonise many remote islands, including those of the Krakatoa group, where they had established themselves within 25 years of the infamous eruptions of 1883, long before any other large vertebrate (Rawlinson et al 1990).

Varanus salvator
Its ability to survive where other animals cannot must be due largely to its very broad diet. Young animals feed largely on insects. Crabs, molluscs and fish form the bulk of the adults' diet in many areas, but they will swallow anything even remotely edible. Snakes, turtles, tortoise, crocodile eggs and young, birds and their eggs, frogs, lizards (including other monitors), rodents, monkeys, small deer, carrion and waste from people, including human corpses and human faeces are all included in the diet (Taylor 1922; Vogel 1979; Deraniyagala 1931, 1953; Grandison 1972; Losos & Greene 1986; Auffenberg 1980, 1986; Rawlinson et al 1990; Gaulke 1989b, 1991a; Traeholt 1993a&b, 1994, Shine et al. 1996)). Water monitors will gorge themselves when given the opportunity, and become so bloated they are unable to offer much resistance to predators (Smith 1931). They are able to eat the notorious marine toad (Bufo marinus) without ill-effect (Gaulke 1991a). Traeholt (1994a) found that water monitors in some areas of Malaysia appeared unable to catch fish but elsewhere fish may form a regular part of the diet (Bennett, in pressb).

The water monitor is said to reach a total length in excess of 3 metres. The largest specimens come from Malaysia, particularly around the Cameron Highlands (Lim 1958; Khan 1969; Anon 1983), where specimens over 250cm TL are sometimes encountered. Jasmi (1988) records that wild specimens can weigh up to 25kg. Thailand is also home to some huge water monitors (Nutphand, Taylor 1963) but elsewhere the water monitor attains smaller sizes; largest found in Java are around 210cm TL, 200cm in Sri Lanka, 203cm in Sumatra and mainland India and less than 150cm on the island of Flores (Vogel 1979; Deraniyagala 1953; Werner 1900; Das 1989; Auffenberg 1980, Sine et al. 1996). In most areas males reach a larger size than females and probably grow faster and are more active. In most populations sexual maturity is attained around 120cm (females) and 130cm (males), but specimens from India can breed at about 100cm TL (50cm SVL), which they can attain after two years under good conditions. In Sumatra Shine et al. (1996) found that males mature at 40cm SVL (100cm TL) and females at 50cm SVL.



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Varanus bitatawa

Varanus bitatawa is the third species of  monitor lizard to be recognised by science that belongs to the "Pandan Biawak" group,  all of which are of at least as great a conservation concern as the Komodo dragon, but receive virtually none of the attention. Pandan Biawak occur only in lowland dipterocarp forest. The first species (Varanus olivaceus or Butaan) was discovered in 1845 and not seen alive by a scientist until the late 1970s. The next species (Varanus mabitang or Mabitang) was discovered in 2001 and in 2010 Varanus bitatawa (Butikaw or Bitatawa) was described. Other species of frugivorous monitor lizards may remain undescribed, but many may have  gone extinct without ever having been recognised.




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