Gray 1845 Perentie
The perentie is the king of the Australian goannas. It is the
largest lizard on the continent and one of the most beautiful
animals in the world. It was once thought to be an uncommon
creature but in recent years the number of sightings has
greatly increased and the known range of the species has
expanded. Despite their large size perenties are extremely shy
and wary animals. Their pattern provides excellent camouflage and it is quite possible to walk
within a metre or so of a large adult without ever being aware of its presence. Because of
their ability to live undetected it is not clear whether perenties have expanded their range in
the last few decades (see below) or whether they have succeeded in remaining unnoticed in
many areas until recently. The perentie is found in arid areas of all mainland Australian states
except Victoria and inhabits many islands off the western coast (Storr 1980). It is absent
from the east coast and the tropical forests of the north , with northern and southern limits at
about 18° and 30° longitude (Gow 1981a; Storr 1980; Houston 1978). They are said to be
particularly common on Barrow Island off Western Australia (Smith 1976; King, et al
The maximum size of the perentie is probably not as great as many authors claim King &
Green (1993) provide a useful discussion of size in this species. Stirling (1912) suggested a
maximum size of almost 230cm. The longest found on Barrow Island by King et al
had a total length of 196cm (88cm SVL) and the heaviest weighed 11.7kg. Butler (1970)
record s a specimen of 17kg with a total length of 193cm from the same island. Stokes (1846)
records that two specimens collected on Barrow Island in 1840 had total lengths of 213cm.
Strimple ( 1988) suggested that one of these animals was the type specimen used by Gray,
which has a total length of only 202cm (Mertens 1958). Many perenties do not grow to such
an enormous size, and the specimens on Barrow Island may grow larger than the mainJand
population (Case & Schwaner 1993). The limited data available suggests that females reach a
smaller maximum size than males, rarely exceeding 140cm TL. Bredl (1987) records males of
180 and 190cm TL, and a female of 130cm TL. A male kept for 14 years in captivity had a
total length of 135cm and weighed 2.9kg, whilst a female kept for seven years measured
116cm TL and weighed 1.55kg (Banks, pers.comm.). A specimen I saw in the Great Victoria
desert measured 52cm SVL (l23cm TL) and weighed 1.8kg when its stomach was empty. It
appears that perenties approaching 200cm in length are the exception rather than the rule,
and that in general few specimens grow larger than 150cm. If specimens of 240cm or more
have ever existed, none seem to have survived to the present.
Perenties are associated with desert regions and particularly with rock outcrops. However
they are also found on grasslands and shrublands devoid of exposed rock. Where caves and
crevices are available the perenties will use them for shelter, otherwise they take refuge in
burrows. Pianka (1994) suggests that the spread of rabbits through the interior of Australia
may have enabled the perenties to occupy many areas that were previously unable to support
them. The perenties certainly prey on mammals to a greater extent than any other Australian
monitor lizard. Stirling (1912) and McPhee (1959) both record that they are able to kill
kangaroos and dismember those that are too large to be swallowed whole with the powerful
forelimbs and claws. Lizards probably account for most of their food especially large and
dwarf goannas including weaker members of the same species (Pianka 1994). They are al so
recorded as having eaten skinks. agamids, seagulls, orthopterans, centipedes and chilopods
and are known to dig up the eggs and young of turtles from sandy beaches (Losos & Greene
1988; Green et al
1988, James, Losos & King 1992; Butler 1970). Much of the perenties'
prey may be caught in open pursuit; they are reported to catch gulls by hiding under vehicles
until the birds come close enough to allow them to be chased down before they can take to
the air (Losos & Greene 1988; King et al 1989). Prey is usually killed by violent shaking.
Horn & Visser (1988) suggest that perenties and sand goannas rarely occur in the same area,
with sand goannas occupying open areas in contrast to the rock outcrops favoured by
perenties. However a perentie we found on a flat spinifex plain in the Great Victoria Desert
had swallowed a desert sand goanna almost the same length as itself and weighing about a
quarter as much as its predator (pianka 1994; Bennett in press).
Stirling (1912) records that perenties will mistake stationary people or horses for trees and
climb up them in their attempts to escape. This behaviour has been observed many times (e.g.
Pianka 1994b, Bennett in press). Perenties do not appear to be active throughout the year.
According to Stirling (1912) they are inactive from May to August and pairs of animals may
share the same burrow. This is confirmed by Hom & Visser (1988) who found a pair of
perenties in a cave at the beginning of October. Pianka (1982) found a large specimen in a
burrow I m deep which he believed had been underground for at least a week.
Perenties are extremely wary animals in the desert, although on Barrow Island they are said
to be accustomed to people and relatively easy to observe. When threatened they often
remain motionless, either in a stiff, extended pose (Bustard 1970) or lying flat on the ground
(Swanson 1976; Hom & Visser 1988). They do not appear to adopt a bipedal stance for
defence, but when running may take to the back legs for short periods (Stirling 1912).
Barrett (1950) published a picture of two perenties engaged in bipedal ritual combat. Similar
photographs by Waite (1929) attributed to V.giganteus
are actually of V.spenceri
When chased perenties will seek refuge in trees, fallen logs, burrows or even in water (Pianka
1982; Hom & Visser 1988). According to Cogger (in Strimple 1988) they adopt an arboreal
existence in some parts of Western Australia. Between September and June perenties are
only active in early morning and late afternoon in Western Australia (Heger & Heger 1993).
A similar bimodal activity pattern has been observed during the summer on Barrow Island
(King, Green & Butler 1989). Perenties maintain active body temperatures of 33-39°C and
can drop to 27°C at night (pianka 1982; King et al
1989). Breeding is said to occur in the
spring (September - October) (Hom & Visser 1988) or summer (November to January)
(Heger & Heger 1993). On Barrow Island mating occurs in Spring and hatchlings appear the
following November (King et al
1989, Butler 1970). Here, activity ranges over ten days of
up to 0.2km2
have been recorded and the same specimen has been found at locations over
5km apart. In the desert the lizards are likely to Cover much larger areas. I followed perentie
tracks made in one afternoon and the early part of the next morning which extended over
2.5km. Pianka (1982) reports that tracks often exceed 1 km. They are able to accumulate
large fat reserves. Stirling (1912) reports that an adult that died after a three month fast still
weighed 7.7kg and contained fat bodies weighing almost 1kg. Details of metabolism are
given by Thompson (1995).
Perenties have been maintained at a number of zoos in the Northern Hemisphere, but captive
reproduction has only been achieved in outdoor enclosures in Australia (Bredl 1987 &
pers.comrn: Bredl & Horn 1987). Up to four adult specimens can be housed in an enclosure
of noor space. The substrate should allow the lizards to dig and large rocks
provided to help them feel secure. Males may be very intolerant of each other but once
compatibility between pairs has been established they may live together for many years
without any violent incidents. However, perenties practise cannibalism regularly in the wild
and care must be taken that only animals of compatible sizes are housed together. Mating and
egglaying occur in late spring and early summer. Up to 11eggs, each weighing around 80g,
are laid in a single clutch, which hatch after about 8 months at 30-32°C with 85% humidity.
Hatchlings weigh 30-50g and measure 14.5-15.5cm SVL (37-38cm TL). If incubated with
higher humidity they would doubtless weigh more. After a month they increase in weight by
ahout 50%. They should be fed a mixed diet of reptiles, birds, mammals, freshwater fish and
large insects, together with vitamin and mineral supplements. A short period of inactivity
during the winter is probably beneficial. Green et al (1986) estimated that during the summer,
when food is abundant (in this case baby turtles containing about 36kJ of energy per gramme
of body weight), adults eat about 36g of prey per kg of body weight, using 118kJ of energy
per kg per day to sustain themselves. During another summer when food was less abundant
they used only about 57kJ per kg per day and consumed 7.3g of food per kg per day.
Perenties have survived in captivity for almost 20 years (Snider & Bowler 1992).