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Varanus gouldiiSand Monitor, Gould's Goanna

By Kirsten McDonnell

Geographic Range

Gould's goanna is commonly found throughout Australia and New Guinea except on Tasmania and in south-eastern Victoria state. (King and Green, 1993; King, 1980)

Habitat

These goannas are widely distributed throughout woodland habitats. They are solely a terrestrial species associated with sandy soils. This goanna is more commonly found in the wet season than the dry season. (Delean, 1981; Doles and Card, 1995; King and Green, 1993; Shine, 1986)

Physical Description

Adult female Gould’s goanna average two-thirds the body length and only one-third the mass of adult males. Adult males are approximately 32 cm in length while females are approximately 28 cm. The lizard is greenish-gray with uniform ringed small yellow spots all over its body. The spots are faint towards the neck but are more prominent on the tail and lower torso. The snake-like head is flat with the yellow pattern on the sides. The bottom quarter of the tail is long and solid yellow.

(Shine 1986)

Reproduction

During the wet season when breeding occurs, the male goanna locates the burrow of a female and builds a burrow of his own a few meters away. Over several days the male and female spend an increasing amount of time together. Eventually, they begin to copulate. They continue to mate over and over again for several days. During this period of intense breeding activity, the pair may share the same burrow. After many days the intensity of copulation declines and the goannas separate and forage independently. When it is time to lay the eggs, the female locates an active termite mound. She digs a tunnel towards the center of the mound 50 to 60 cm deep. At the end of the tunnel she digs a large cavity. The female then sits on the top of the mound and lays 10 to 17 eggs into the tunnel. Afterwards she refills the tunnel, and the termites reconstruct the mound around the goanna eggs. The termites regulate the temperature and humidity, so this is an excellent place for development of the eggs. Delayed fertilization has been recorded in this species.

Lifespan/Longevity

  • Average lifespan
    Status: captivity
    18.3 years
    AnAge

Behavior

In this diurnal species, males have larger territories and are more active than females. The entrance of a goanna burrow is often beneath a flat rock, a small shrub, or a fallen log. Gould’s goanna often use the warrens of introduced rabbits for shelter instead of constructing their own burrows. The burrows are important for providing protection from predators and weather.

While foraging, goannas' attention is focused on digging for prey, so they expose themselves to predation. When walking, goannas carry their bodies high off the ground and only a small portion of the tail near the tip touches the ground. While running the tail is lifted completely off the ground. When approached the goanna takes on a threatening position by arching its back, inflating its neck, and hissing loudly, and it can produce powerful side-swipes of the tail. The species is also reported to sometimes rear up on its hind legs in response to a threat.

To get warmer the Gould’s goanna basks in the sun, and it burrows to cool down.

Food Habits

All varanids are carnivorous and active predators. Gould’s goannas eat primarily mammals and reptiles but will also eat birds, amphibians, reptile eggs, insects, and crustaceans. Much of the vertebrate portion of their diet is probably scavenged from animals killed on the road. The goanna forages over long distances and often digs for prey in loose soil and decaying vegetation. They obtain most of their water from their food. Goannas walk with their snout held close to the ground while hunting for food. The long forked tongue flickers in and out transferring scents to the Jacobson’s organs. This way they can rapidly locate hidden prey, even if it is underground. They then use their sharp claws as well as their snout to dig out the prey. Cannibalism also occurs in the Gould’s goanna. Often this involves feeding on carrion.

Economic Importance for Humans: Positive

Many goannas are used for food by Aborigines. They are also important animals in many Aboriginal cultures.

Economic Importance for Humans: Negative

This reptile does no economic harm.

Conservation Status

Varanids are protected from exploitation by state, federal, and international legislation. The conservation status is quite stable. Their largest threats are poachers, vehicle traffic, and raptorial birds. Habitat alteration and pollution must be kept to a minimum in order to maintain the species. (King and Green 1993)

Contributors

Kirsten McDonnell (author), University of Michigan-Ann Arbor, Dea Armstrong (editor), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

native range

the area in which the animal is naturally found, the region in which it is endemic.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

sedentary

remains in the same area

solitary

lives alone

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

References

Delean, S. 1981. Notes on aggressive behavior by Gould’s goannas (-Varanus gouldii-) in captivity. Herpetofauna, 12(2): 30.

Doles, M., W. Card. 1995. Delayed fertilization in the monitor lizard Varanus gouldii. Herpetological Review, 26(4): 196.

King, D. 1980. The thermal biology of free-living sand goannas (Vananus gouldii) in southern Australia. Copeia, 1980(4): 755-767.

King, D., B. Green. 1993. Goanna: The Biology of Varanid Lizards. Kensington, Australia: New South Wales University Press.

Shine, R. 1986. Food habits, habitats and reproductive biology of four sympatric species of varanid lizards in tropical Australia.. Herpetologica, 42(3): 346-360.

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