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Varanus olivaceus Print E-mail

Little is known of the breeding habits of Grey's monitor. Reproductive activity occurs mainly between June and September, when day length is longest, temperatures lowest and rainfall highest. It is interesting that in Gray's monitor egg production seems not to depend on the use of accumulated fat, for fat bodies are smallest whilst ovaries are growing at their fastest rate. The first behavioural change associated with reproduction is bipedal combat between males which occurs as testes reach their greatest weight. Copulation has been observed in captivity and appear to be very gentle compared with that of other species. There is some evidence that long term pair bonding may occur in this species (see Chapter 5).

In the wild a single clutch of up to 11 eggs is produced between July and October. The eggs weigh 40-50g and measure about 6.7X3.6cm. They account for up to 18.6% of female body weight. In captivity two clutches of eggs (total 14) may be laid within four months of each other and Auffenberg believed that this may occur in the wild as well. Nothing is known of their nesting habits, but tree hollows seem the most likely nest sites. Nor is there any good data on the length of incubation. The smallest specimens are found from May to July, suggesting that the eggs may not hatch for over 300 days.

The skin of Grey's monitor is rarely used for commercial trade, but the meat is popular and the fat particularly so, because it is less liable to breaking down at high temperatures than that of the much more easily obtained water monitor. Apart from pythons, mankind appears to be the only important predator of the adult lizards. On account of its very restricted distribution Gray's monitor has been placed on Appendix 1 of the CITES legislation and export of animals for commercial purposes is outlawed.

In captivity this species poses a number of unusual problems. A large, high enclosure should be provided with plenty of hiding places both above and below the ground. An enclosure with 9m2 of floor space is sufficient to house a pair, but animals are often intolerant of each other or may refused to feed unless housed singly. They enjoy being sprayed with water and should be provided with frequent showers. Unlike most monitor lizards Gray's monitor does very little digging and appears not to ingest much substrate with its food. The fruit eaten by Gray's monitor are almost all endemic to the Philippine Islands and none are suitable for use as human food. Thus the frugivorous portion of this lizard's diet may prove almost impossible to replicate in captivity. It has been established that captives will survive for long periods on a diet of animals alone (Behler, Mitchell, pers. comm.) but it is unlikely that successful breeding can be accomplished on such a diet.

The only report of breeding comes from the Dallas Zoo (Card 1994a,b 1995c) where pulverised fruit, vegetable oil and fructose are used to supplement a diet of rodents. These additives must be injected into the prey animals; the only fruits taken voluntarily in captivity are grapes. Females are capable of producing more than one clutch of eggs per year, but to date only a single, short-lived juvenile has hatched, after 219 days at 28oC.

 

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The Butaan Project
The Butaan Project - Research
butaan3.jpgThe only obligate fruit-eaters among reptiles are three species of monitor lizard that live in the Philippines. Frugivorous vertebrates tend to be able to fly (almost all are bats and birds) and so these lizards have a unique ecological role as highly specialized and relatively immobile fruit eaters. Before this project started, the only studies of this unique giant and endangered lizard had involved killing the animals. We have developed a set of techniques that allow us to learn about these animals in a completely non-destructive way.
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