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Varanus varius Print E-mail

Mating occurs during the summer in temperate regions. Up to six males may court a female at the same time and generally only the largest is successful (Wilson 1987). Mating has been observed taking place continuously over a period of several hours (Tasoulis 1983; Carter 1990). Maximum clutch size is usually given as 12 (e.g. Cogger 1959, Bustard 1970) and mean clutch size of 8 has been reported (Carter in Boylan 1995) but clutches of 19 eggs have been recovered from termite mounds (Boylan, 1995). Eggs usually weigh 50-65g (Bredl & Schwaner 1983, Horn 1991), representing a total possible clutch mass of over 1000g (but see below). The eggs are deposited in an active termite mound when these are available, either on the ground or in a tree (e.g. Longley 1945; Cogger 1959, Bustard 1970, Tasoulis 1992). In New South Wales eggs overwinter and hatch after 6-7 months. How the hatchlings escape from their termite mounds has been a matter of some debate. They seem to lack the strength to break through the tough outer wall of the mound. Incidences of adult lace goannas excavating nests is high during the spring whilst the eggs are hatching and this behaviour may serve to release the youngsters (Carter 1989, Boylan 1995). However at present their is no published evidence that the maternal individual remembers the location of her nest and returns there after many months to release her young. A television documentary which purported to show the release of hatchlings from a termite mound by their mother used broad artistic license (Marven 1990). After their escape/release the youngsters may remain around the nest for a week or more before dispersing. Like other monitor lizards the youngsters are more arboreal in habit than the adults. Where termitaria are absent the eggs are deposited in burrows or possibly in hollow logs (Cogger 1959, Houston 1978). Lace monitors may remain in one area for most of their adult lives. Frauca (1966 in Greer 1989) records a specimen that lived in the same tree for several years. Similarly females may use the same termite mound regularly as a nesting site. Where suitable termitaria are in short supply they may be vigourously defended against other females (Carter 1989, Horn 1991). The very large clutch of 19 eggs reported by Boylan (1993) could represent the eggs of more than one female, suggesting that nesting sites may be shared under some circumstances. Weavers (1988) considered that in temperate areas lace goannas may reach great ages (well over 20 years), based on their extremely low growth rates. In captivity they are known to live for over 15 years (Flower 1937; Kennerson 1979).

The thermal biology of the lace goanna has been investigated in some detail. They are able to raise their body temperatures by up to 2oC above ambient temperatures using heat generated by respiration (Bartholomew & Tucker 1964). Critical thermal maximums of 43-44.5oC have been established and below 5oC they are completely inactive (Spellerberg 1972). Green & King (1993) record activity temperatures of 32.8-36.4oC which can drop to about 21oC at night.

Reproduction and artificial egg incubation have been reported by Markwell (1983) Bredl & Schwaner (1983) and Boylan (1995). Outside Australia only one captive breeding has been reported (Horn & Visser 1990, Horn 1991). An enclosure with at least 2.5m2 of floor space is required to house an adult specimen. As much height as possible should be provided to allow climbing. Hoser (1993a) maintained a group of seven adults in a 90m2 outdoor enclosure. Best results have been obtained with animals raised in captivity from an early age and originating from the same location. They do well on a mixed diet of insects, small mammals and birds with plenty of extra vitamins and minerals. Females may produce more than one clutch of eggs per year and need large amounts of food. Horn & Visser (1990) record that a female ate 15 chicks, 20 mice and 2 rats with a week of laying eggs! Pairs often tolerate each other very well, but separating and reintroducing animals may be necessary to trigger courtship behaviour. Larger animals will kill and consume smaller ones (Hoser 1993a). A nesting box (as described in Horn 1991) should be provided for the female to deposit her eggs in. Depending on incubation temperature they hatch after 184-317 days (Markwell 1983, Bredl & Schwaner 1983). At a constant 29oC they hatch after about 235 days (Horn & Visser 1989, Horn 1991). Youngsters measure 28-36cm TL and weigh about 35g, but significantly smaller hatchlings of 16-23g were recorded by Weavers (1988) and Boylan (1995). It is not clear whether this is due to incubation conditions or related to the size of the female. Hatchlings seem to prefer vertebrate prey to insects and can grow rapidly, reaching 30cm SVL and over 300g within ten months (Horn 1991, Horn & Visser 1991). The environmental conditions provided for lace goannas must take into consideration the natural habitat of the animals, which varies from moist and tropical in the north to seasonal in the south.




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