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  Section: Monitor Lizards » The Monitor Lizards Of the World
 
 
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Varanus Tristis

 
     
 
Mournful goanna, black-headed goanna, freckled
goanna, racehorse goanna.
Varanus tristis tristis Boulenger 1839
Varanus tristis orientalis Fry 1913.


VARANUS TRISTIS
The mournful goanna is perhaps the most widespread of the Australian monitor lizards. It is found throughout the continent except for the extreme south and south-east and occurs on many northern islands. Christian (1981) reports that they are absent from Victoria and restricted to arid parts of western New South Wales. Fitzgerald (1983) records a specimen from nonh-eastern New South Wales. According to Houston (1979) they are not well known in South Ausualia. Low (1978) records their presence on Magnetic Island off the northern coast of Queensland. Storr (1980) gives a list of locations in Western Australia and Maryan (1989) found them at Peak Charles. Western Auscralia. I visited Peak Charles in 1991 , a few months after an extensive fire, and could find no sign of them. Records of V.tristiis orientalis in New Guinea and adjacent islands (Menens 1950) probably refer to the V.timorensis type animals discussed previously. V.tristis centralis (Mertens 1957) is an obsolete name for V.tristis orientalis (Mertens J958).

The name mournful goanna is somewhat misleading. It refers to the entirely black colouration of the populations of V.tristis tristis around Perth, Western Ausualia (tristis = sad). Mournful goannas from warmer (i.e. more northern) areas become increasingly less sombre in appearance. The freckled goanna V.tristis orientalis was described from animals collected on the Burnell River, Queensland. These animals lack the melanistic pattern of the mournful goannas and can further be distinguished by the less spiny scales on the tail (Fry 1913; Mertens 1958). Storr (1980) remarked that the few specimens he examined from Queensland differed in scalation from Western Australian animals, but did not give details. In the literature therefore, animals without black colouration tend to be described as V.tristis orientalis. The subspecies appear to be sympaoic in many areas and both are found on the eastern coast of Queensland (Christian 1981). Hatchlings of both varieties are brightly coloured, but freckled goannas retain most of their juvenile pattern whilst in mournful goannas the pattern darkens and is replaced with varying amounts of black as the animals grow. Mournful monitors reach a slightly larger size than freckled monitors (about 80cm TL vs. 60cm TL). In the deserts both sexes reach sexual maturity at 20cm SVL. A specimen 25cm SVL weighed 307g, another 25cm SVL weighed 150g and a hatchling of 7cm SVL weighed just over 4g.

The mournful monitor is an excellent climber. Where uees are available the lizards spend most of their time concealed beneath bark or in cree hollows. Where uees are absent, or are occupied by other species, the goannas will live in rock crevices or under slabs of stone. Fyfe (1979) notes that at Ayres Rock they are often seen around buildings. They are often found along rivers and are known from forests, woodlands and scrublands but are also widespread in desens. They are probably absent from the rainforests. Little is known about their way of life in tropical Australia.

In the deserts of Western Australia mournful goannas shelter in Eucalyptus trees and move directly from tree to tree, exploring burrows en route in search of food. They are most active during the spring and often cover over
a kilometre per day accumulating large fat reserves to sustain them through six or seven months of inactivity during the winter. Other lizards are their main prey, including other goannas, skinks, geckoes and agamids. They often swallow large agamids over a quarter of their own body weight and are able to swallow the heavily protected thorny devil, Moloch horridus. They also raid birds nests for eggs and fledglings and collect a variety of invertebrates including orthopterans, beetles, ants and stick insects. Mating occurs in November, when pairs of lizards have been found sharing the same tree. Large numbers (6-11 but sometimes as many as 17) of small eggs are laid in December which hatch in February or March, when the adults are relatively inactive. Nothing is known of their nesting habits nor of the habits of juveniles, but very young specimens have been found considerable distances from trees (Pianka 1971 , 1982, 1994; Losos & Greene 1988; James, Losos & King 1992; Bennett 1993).

The thermoregulatory behaviour of the mournful goanna must be extraordinary. Body temperatures as high as 47.3°C hav e been recorded in the wild (Pianka 1994)! The ability to tolerate such high temperatures is very rare in the animal kingdom. In general however, mournful goannas maintain lower active body temperatures than other desert goannas. The amount of black colouration probably has a major effect on the rate of heating in this species. It would be very interesting to compare the thermoregulatory behaviour of melanistic and non-melanistic forms.

Outside the deserts mournful goannas may be less arboreal than their freckled counterparts. According to Christian (1981) the former is more suited to a terrestrial existence than the latter, on accounts of its larger size and greater speed. In areas of Australia where they occur together Shine (1986) considered V.tristis to be less arboreal than V.scalaris and have a narrower range of habitats. Schmida (1985) listed the most important items of prey as frogs and small mammals. Swanson (1976) claimed that insects, mice and lizards are preferred foods. Both Christian (1981) and Fyfe (1979, 1980) report that V.tristis can curl its tail over its head and body when basking or walking. The purpose of this unusual behaviour is not understood .

Freckled goanna
Freckled goanna
The name racehorse goanna has been used to describe several species of Australian monitor lizard, including V.tristis. This species may have most claim to the name, because they can move at phenomenal speeds, especially when they are very warm. Their speed, arboreal habits and secretive behaviour make them very difficult creatures to observe in the wild. Pianka (1971) notes that this species drags its tail base along the ground when walking, producing a distinctive trail. It would be interesting to investigate whether the lizards leave any chemical clues to their presence by this means.

In captivity freckled monitors have reproduced in captivity on several occasions (Broer & Horn 1985; Eidenmuller 1989; O'Dell 1992 & pers.comm., Lambertz 1995). Males of both subspecies have clusters of spines on either side of the tail base which are very much reduced or absent in females. The animals tolerate each other very well and a pair can be housed comfortably in an enclosure with 1m2 of floor area. Large amounts of climbing space are desirable but do not appear to be essential. A diet of various large insects and small rodents is suitable, washed down with plenty of vitamins and minerals. Females should be gorged with food throughout the breeding season to enable them to produce large numbers of strong, healthy eggs. Darker animals in particular may benefit from cooler winters with a shorter photoperiod. Mating occurs in the spring and two clutches of eggs can be laid within a couple of months and up to four clutches can be produced over a year. They hatch after 95137 days at 27-29°C. Given good feeding (small insects and portions of rodents) they can multiple in weight within three months and attain sexual maturity within 2 years.

Attribution / Courtesy: Daniel Bennett. 1995. A Little Book of Monitor Lizards. Viper Press U.K.
 
     
 
 
     



     
 
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