Movement & Shelter

For most of the year monitor lizards move only to find food. When prey are abundant the lizards move much more than when it is in short supply. Male monitors reach the peak of their activity during the mating season (when they are seeking out females) whilst females are most active immediately afterwards as they search for nesting sites. At all times movement is resuicted by the need to thermoregulate and conserve water and, conversely, maintaining suitable body temperatures and reducing water loss are achieved largely through movement. Estimates of home range and daily distance travelled have been recorded for many species, but direct comparisons between them are impossible to make because of differences in the methods used and the season, climate, type of habitat, size of the lizards and duration of the study. Almost all studies suggest that for most of the year males are more active than females and that as a result males appear to be more common (e.g. Gaulke 1989b). Their higher activity levels are also responsible for their larger food in takes and faster growth rates. Even within small populations some individuals cover much greater distances than other of the same size and sex. The best data for movement patterns in wild monitor lizards comes from Auffenberg's (1981) study of the Komodo dragon¹, a very large lizard living on a small island. The results show that whilst some adult monitors may remain in the same area for most of their lives and are very well acquainted with the local topography, others may be transient and rarely remain in one place for more than a couple of days before moving on. Such differences between individuals may be common amongst monitor species. Virtually nothing is known of the movement patterns of juvenile monitor lizards. Many young Bosc's monitors remain in the same small fields for a month or more if food is plentiful and none have been observed to rravel more than 150m in five weeks (Bennett & Akonnor 1995).

Many monitor lizards are extremely adept at standing on their hind legs. This posture has been observed in many larger species, but not in any of the dwarf monitors. A bipedal stance is adopted during ritual combat or to gain a higher vantage point from which to survey the surroundings. Some species also stand upright when threatened by tall predators, but this behaviour is limited mainly to some of the larger Australian goannas, particularly Gould's goanna.

When monitor lizards are not active they remain in shelters. Some species make use of tree hollows, thickets of vegetation, crevices in rock, termite mounds or bodies of water for shelter, but it is burrows that are of particular interest, for they provide the monitor with the opportunity to adapt the retreat to their own particular tastes. Unwilling to expend any more energy than is absolutely necessary, monitors will steal the burrows of other animals and adapt them accordingly rather than go to the trouble of undertaking the entire construction themselves. Preferred sites are usually under rock, amongst large roots or in some other sheltered position. To us, a burrow is merely a hole in the ground but to a monitor lizard it is a haven to which retreat may be made from the everyday pressures of reptilian life. As well as providing shelter from extremes of heat and cold and acting as a humidity trap, the humble burrow provides a refuge during periods of inactivity (when digesting large meals, during inclement weather or just out of sheer laziness), a hideaway from predators, a trap for prey, a cozy lovenest during the breeding season and, if required, can be adapted to make a nest for eggs. Monitor burrows vary greatly in size and shape and descriptions of the burrows of many species have been published. The deepest² are those of desert monitors, such as the Caspian monitor that has to endure winter temperatures as low as 30° C. Such burrows are more than a metre deep and can be many metres long. They are probably constructed by the combined effort of many generations of monitors (Bennett 1992b). Storr's goannas in tropical Australia are said to dig and cohabit shallow networks of burrows whilst several species may shelter in shallow burrows that provide an emergency exit through the terminus if the entrance is blocked. (Bustard 1970).

Patterns of burrow use by Komodo dragons, Bengal monitors and water monitors are particularly well documented (Auffenberg 1981. 1983a; Traeholt in press^a). Monitor lizards rarely use the same burrow twice in as many nights and because they are not territorial a good burrow may be used by many different lizards in the course of a year. Generally the burrows are used by one monitor at a time, although there are several records of a pair (presumably a male and female) found huddled together in the same hole. Other animals may also enter the burrow for shelter and stand a good chance of being gobbled up by the landlord. Whittaker (1970) reports finding a cobra and a monitor lizard sharing the same burrow without adversity.

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