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Varanus griseus Print E-mail

The deserts inhabited by the grey monitor are subject to great variations in seasonal temperature. In Israel males are active from late April and early May until July or August whilst females remain active until late October or November (Stanner & Mendlessohn 1983, 1987, 1991). The lizards stick to well defined home ranges and those of males are much larger than those of females (about 1km2 compared with 0.3km2). Females maintain the same home ranges for at least several years whilst males change theirs annually. Foraging distances of 2km or more are common.

In Algeria the monitors have two periods of activity, from April to June and a shorter period during October. During the winter and hottest part of the summer they remain below ground. Home ranges were estimated at 1-4km2 (much larger than those in Israel, presumably because of lower food densities) and foraging trips of up to 8km per day were recorded (Vernet 1982; Vernet et al 1988a). These studies suggested that males were not particularly more active than females. In the same parts of Algeria Saint Girons & Saint Girons (1959) estimated home range size as 2-5km2. Although the lizards have well defined home ranges they are neither territorial nor do they consistently use the same shelters and basking sites. In Syria grey monitors are found only in spring and early summer (Martens & Kock 1992) whilst in Mauritania active grey monitors have been seen as late as November (Linley. pers. comm.).

In Algeria grey monitors maintain active body temperatures of between 35-38oC. At temperatures below 20oC the lizards become inactive and hibernation is induced at about 17oC. The lizards voluntarily allow body temperature to get no higher than 41oC and die at temperatures of between 44-47oC (Vernet et al 1988b). Grenot (1968) (reviewed in George (1986)) found that the grey monitor is able to maintain a body temperature of 42oC for up to four hours at an ambient temperature of 50oC. In warm weather the lizards can raise their body temperatures by as much as 0.5oC per minute by basking (Francaz et al 1976, 1978). Although the seasonal activity of the grey monitor depends largely on  temperature, Vernet et al (1988a) believed that the daily activity of the lizards depended more on prey availability than climate (similar findings have been reported for V.albigularis). Lemire & Vernet (1985) report that the grey monitor has salt glands which allow it to minimise water loss (see Chapter 3).

In Israel grey monitor burrows are said to be an average of 125cm long and just 30cm deep. They vary greatly in shape (Stanner 1985). These burrows are probably used only during the warmer part of the year. During the winter the lizards may take shelter in much deeper refuges. An Algeria they have been recorded from burrows as deep as 300cm (Mammeir, pers. comm.). Schmidt & Marx (1957) record that in Egypt grey monitors dig very deep and complex burrows with several openings. Andres (1904) records that a captive specimen escaped by digging a very deep burrow under a garden wall.

Little is known about the breeding behaviour of the grey monitor lizard. In Algeria, Tunisia and Israel mating occurs during May and June and eggs are laid in June and July (Vernet, Lemire & Grenot 1983; Mertens 1942; Stanner 1985). There are no records of nesting sites. In Israel females' weight may be reduced by as much as 47% after egg laying. Their continued activity into the early winter is probably due to their need to accumulate large fat reserves both to maintain them through the long period of inactivity and to provide energy to form eggs for the next breeding season.  Hatchlings appear in March of the following year, but an incubation period of eight months seems unlikely (see below). The habits of the juveniles remain completely unknown. Thilenius (1897) suggests that females may return to the nest site after oviposition, but makes no attempt to explain why.

The Caspian monitor (V.griseus caspius) is the largest race of the desert monitor. It is considered to be in danger of extinction and is one of the few monitor lizards whose commercial trade is completely outlawed. Despite this they are regularly offered for sale and, a few years ago at least, were not an uncommon sight in Moscow's pet market. The Caspian monitor is found from the east coast of the Caspian Sea throughout the deserts of central Asia (including many islands of the Aral Sea as far as about 69o east and 46o north.  In the south it is found at elevations of up to 800m in the Kopet Dag mountains and extends into northern Iran, western and southern Afghanistan as far as western Pakistan. It is best known from the states formerly affiliated to the U.S.S.R.; Turkmenistan, Khazakstan, Uzebekistan, Kirgizstan and Tadzikistan. It previously occurred in the Fergana Baisin but is now extinct there and has also disappeared from the Golodnaya and Dalverzinskaya regions of Uzebekistan (Leviton & Anderson 1970; Yadgarov 1968, et al 1988; Ataev 1987; Shammakov 1981; Makayev 1982). Specimens have also been recorded from as far east as Tashkent (Kulagin in Nikolskii (1915)) but they do not occur there now.

The Caspian monitor reaches a maximum size of about 140cm. Males tend to be longer than females (largest male recorded from Turkmenistan by Shammakov (1981) was 58.5cm SVL, largest female was 46cm) but not much heavier (heaviest male was 2,850g heaviest female 2,700g). The Caspian monitor is distinguished from other races of V.griseus largely by the shape of its tail, which is laterally compressed in contrast to the tails of other races, which tend to be more or less rounded in cross section.

The Caspian monitor is found in both sandy and clay deserts. They avoid areas of dense vegetation but are found in sparse woodland. Those from clayey areas are often a distinctive reddish colour (Bennett 1992a). On Islands in the Aral Sea they are found in salt marshes as well as sandy areas. They are sometimes found on the edges of agricultural land, but, because they are often killed when encountered, Caspian monitors tend to be very uncommon in areas of human habitation. In abandoned settlements they often inhabit cracks in wattle and daub houses. Caspian monitor lizards reach their highest densities where colonies of mammals are abundant. Makeyev (1982) records 9-12 specimens per km2 on the edge of Karabil, close to Karamet-Niyaz (Turkmenistan) and in the Saihan Valley (Uzbekistan), 5 specimens per km2 in southeastern Turkmenistan and 3-5 specimens per km2 on clay desert at  Kara-Kala. Over most of the sandy desert densities are estimated at 2-3 lizards per km2, whilst in river valleys numbers drop to 1-1.5 specimens per km2.


 
 

 

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Butaan start to visit fruiting trees before they are large enough to swallow the fruits. They make repeat journeys to trees, perhaps to reinforce memory of the position of the tree. If the youngster survives it may continue to use this tree for many decades. Fruiting trees like this are a vital resource for entire populations of butaan. Learn more >


 
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Since 1999 the Butaan Project has been studying the rare, endangered, and unique fruit-eating monitor lizards of the Philippines.  Butaan is just one of several races of frugivorous monitor lizards in the Philippines ("Pandan Biawak"), 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 (Butaan) was discovered in 1845 and not seen alive by a scientist until the late 1970s. The next species (Mabitang) was discovered in 2001. Other species remain undescribed, and some may have gone extinct without ever having been recognised.

 

 

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