Varanus giganteus


The perentie, Varanus giganteus, is Australia's largest species of lizard. These lizards can sometimes exceed two meters in total length. They are top predators, eating many other species of vertebrates, including smaller individuals of their own species as well as other species of monitor lizards.

Monitor lizards are large and impressive. They are often the centerpiece of reptile house exhibits. Monitors are not particularly tractable research subjects, but these magnificent lizards have received an extraordinary amount of attention from devoted students. All but one species, the frugivorous Varanus olivaceus of the Philippines (Auffenberg 1988), are active predators that eat quite large prey relative to their own body size. Many monitor lizards are top predators. Some species are aquatic, others terrestrial, while still others are saxicolous and/or semi-arboreal or truly arboreal. Monitor lizards live in a wide variety of habitats, ranging from mangrove swamps to dense forests to savannas to arid deserts.

Currently, 53 extant species are recognized. All occur in Africa, Asia, southeast Asia, and Australia (the new world is sadly impoverished). Some 27 described species are found in Australia, including one lineage that has evolved dwarfism (hatchlings of the smallest species V. brevicauda weigh only one gram). A Pleistocene fossil monitor from Australia is estimated to have reached 5 m in total length and to have weighed over 600 kg. Although monitors are morphologically conservative, they vary in mass by five orders of magnitude. There is proportionately almost as much difference in mass among species of monitor lizards as there is between a mouse and an elephant. No other terrestrial animal genus exhibits such a range of size variation (Pianka 1995).

Sands constitute a natural event recorder, leaving a record of what creatures have moved past. Strong winds regularly dull and erase all tracks. Although it took quite a while, I eventually became fairly skilled at reading the record in the sand. Tracks are difficult to see during mid-day when the sun is high or on overcast days. Morning and afternoon are prime times for tracking when the sun is low in the sky and shadows are long. Tracks are best seen by looking into the light. After a bit of experience, one begins to be able to judge the "run" of the track, that is where the animal is headed. It is almost like becoming the lizard yourself. This allows one to move ahead quickly, cutting the track at intervals, to find the lizard rapidly. You can even tell the approximate age of a track by its crispness and whether or not other tracks, say those of nocturnal species, cross over the track in question. Nothing is much more exciting than finding a crisp new track less than an hour old, for you know that the maker of that track is close by at the end of the track. It is like finding a line guaranteed to lead you to a neat lizard! On a very hot trail I always walk as quietly as possible, barely breathing, scouting ahead to look for the lizard itself. Tracking large lizards across sandy areas has become one of my favorite pastimes. You can learn a great deal about wary unobservable species such as Varanus in this way. It is an incredible thrill when the track suddenly becomes the magnificent animal, captured in mid-stride and frozen in time. More often than not, however, before you see it, the animal breaks into a run and dives down a hole or climbs up a tree and escapes into a hollow. The track of a running animal is often harder to follow than that of one walking.

Statements about Varanus giganteus to follow are based upon impressions I have gained while following literally hundreds of kilometers of giganteus tracks on foot. Individuals usually cover great distances when foraging. I have often followed a fresh track for distances of several kilometers. Tracks indicate little tendency to stay within a delimited area; home ranges of these lizards would appear to be extremely large.

The perentie, Varanus giganteus, attains a total length of more than 2m. They have been hunted by Aborigines and are exceedingly unapproachable. Their food may once have included small hare wallabies and other mid-sized marsupials, many of which have become extinct. Nowadays, perenties feed on other species of lizards and on introduced European rabbits (several scats examined contained large amounts of hair). An assistant and I flushed the stomach of a medium-sized lizard, which contained a half-digested Varanus gouldii, estimated probable body mass about 400 g, about 20% of the perentie's overall body mass.

During 207 days in the field in over 16 months in 1966-68, I encountered only two live perenties, one at the edge of sandplain country near a breakaway and the other at a tor area south of Sandstone, and found no evidence of perentie tracks in the sandy desert. In 1979, I found one perentie, far away from rock outcrops at my sandridge desert site Red Sands. This animal had several deep burrows. A decade later, during 1989-91, perenties were more abundant at Red Sands. I tracked four different individuals, and judged that several others were present by the size of their footprints and lengths of stride. In addition, I saw a dozen other individuals, several in sandy habitats, while driving to and from my study sites. I speculate that perenties have increased in abundance in the Great Victoria desert over the past 25 years, probably in direct response to the increased abundance of introduced european rabbits (Oryctolagus cuniculus). Rabbits were scarce in the Great Victoria desert during 1966-68, were moderately abundant during 1978-79 (pers. obs.), and had become quite common by 1988-93. Perenties could also be expanding their geographic range southwards and eastwards. I have positively identified two very large individuals crossing the road between Menzies and Leonora, one near Lake Goongarrie (30 o 01' S x 121 o 10' E), and the other 46 km South of Leonora.

References

Pianka, E. R. 1982. Observations on the ecology of Varanus in the Great Victoria desert. Western Australian Naturalist 15: 37-44. Download pdf

Pianka, E. R. 1986. Ecology and Natural History of Desert Lizards. Analyses of the Ecological Niche and Community Structure. Princeton University Press, Princeton, New Jersey.

Pianka, E. R. 1994. Comparative ecology of Varanus in the Great Victoria desert. Australian Journal of Ecology 19: 395-408. Download pdf.

Pianka, E. R. 1995. Evolution of body size: Varanid lizards as a model system. American Naturalist 146: 398-414. Download pdf.


The Lizard Kings. PBS NOVA Video showcasing Eric R. Pianka's research on monitor lizards in the Great Victoria Desert of Western Australia.
Watch this video on line.

To read about other Varanus in the Great Victoria desert of Western Australia, click Desert Varanus.

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