Central Bearded Dragon

Introduction

You may catch a glimpse of these sun loving dragons on the side of an outback highway, or patrolling for insects in a woodland clearing. Like other species of Bearded Dragon, this lizard relies on more bluff than bite; trying to appear larger and spikier than it really is to any potential predator.

Identification

The Central Bearded Dragon has a low wide body shape, allowing it to hug surfaces when it is lying down. When walking however it walks with a high gate and can move with considerable speed. The elongated spinous scales around the rear of the lower jaw and lower sides of the body appear very spiky but are actually quite rubbery and only intended to make the lizard appear unappealing to predators. The tail is almost the same length of the head and body. The head is triangular in shape and can appear to have a striped pattern along the jaws. Unlike the Eastern Bearded Dragon which is mostly grey, the Central Bearded Dragon can also be found in a variety of colours, including shades of red, brown and yellow. These colours normally match the colour of soil that occurs in the dragon’s habitat.

Generally males have larger heads and are brighter in colouration than females.

Habitat

The species’ habitats include temperate to tropical arid to semi-arid woodland, shrubland and hummock grassland (with scattered trees).

Distribution

The Central Bearded Dragon occurs in a band across the semi-arid interior of eastern Australia, including western New South Wales and the Riverina region, wherever suitable habitat can be found.

Seasonality

In late spring (November), males are seen much more commonly than females.

One female was observed basking in winter (August) when the air temperature was 15º C. During the hottest part of the activity season, the dragons are usually active only during the early morning and late afternoon.

Feeding and diet

These omnivorous lizards feed on vegetation including fruit and leaves in the wild, as well as any invertebrates (including ants and beetles) and small vertebrates (such as lizards) that they can catch.

The captive diet for this species at the Australian Museum is provided in three feeds within a period of a week. These consist of a small feed of chopped vegetables on one day, a small serving of kangaroo mince on another day as well a hand full of cockroaches and crickets for the third feeding. The timing and order of the diet is changed around to simulate natural conditions and prevent stereotypical behaviour (where an animal will have predicable activity patterns and essentially be waiting to be fed). This food is supplemented with calcium and vitamin powder to ensure that a nutritionally balanced diet is provided.

When a prey item or edible piece of vegetation is located the mouth opens rapidly allowing the tongue of the dragon to lunge forward. The sticky tongue pulls the food item into the mouth where it is held by the teeth and strong jaw muscles. These then work quickly to kill and or break up the animal or plant before being swallowed.

Central Bearded Dragons will drink from standing free water such as a dish in captivity, however they also have another method of drinking which, although observed in an outdoor enclosure, may also be used in the wild. During light rain, an individual stood up on its rear limbs with its head and tail sloping down and as water ran forward over its body to its head and snout, it would lick it. The lizard held this position for 20 to 30 minutes.

Other behaviours and adaptations

Central Bearded Dragons are primarily diurnal, however they are sometimes seen out on roads after dark, especially after hot days. This suggests that the species may be more active after dark than previously realised.

The species basks to maintain preferred body temperature. When the animals’ body temperature rises to relatively high and presumably dangerous levels, they open their mouths to varying degrees, presumably in order to cool the blood passing through the head by evaporative cooling from the moist membranes of the mouth.

Like other Bearded Dragons, this species is an adept climber, and can usually be found on tree stumps, tree branches, boulders and fence posts. From the elevated position the lizard will bask in the sunlight and keep an eye out for potential predators, prey, rivals and mates. During extremely hot periods, individuals may remain perched above ground for long periods. For example, on one occasion a male remained perched in the same tree 3 m above the ground for three weeks.

When alarmed the lizard faces the intruder with mouth wide open and beard puffed out to make the jaw appear larger. The dragon inhales air rapidly to expand the body, making the spiked sides of the animal appear rigid and the overall size seem greater to the aggressor.

The lizards can undergo rapid colour change. For example, one specimen changed from predominantly all yellow to almost completely black in no more than a few minutes. Mature males often change the colour of their lower jaw (beard) from the normal colouration to black. When puffed up in a defensive pose, the ‘beard’ then appears more striking.

Communication

Apart from a low hiss when threatened, Bearded Dragons do not vocalise. Communication is achieved through posturing, colour display, head bobbing and arm waving. A distinct hierarchy can be seen when these usually solitary lizards congregate at prime basking sites and at times of abundant food. Dominant animals will head bob and inflate the beard when challenged as a sign of fitness. Submission is signalled by waving the forearm, which generally defuses the confrontation, however if one does not back down the animals will then circle each other and a standoff or fight will ensue.

Head bobbing is expressed by different animals for different social reasons; a slow bowing is often used by adult females to signal submission to a male, a fast bob combined with an inflated and blackened beard is used by males to signal dominance. Violent 'whole body' bobbing is used by males just before mating. Arm waving is used by both sexes; males use waving to show submission to a dominant male, females will arm wave to show responsiveness to a male, combined with a slow head bob.

Breeding behaviours

Males engage in combat involving beard flaring, signalling, circling and tail biting to establish mating rights after the winter cooling period. Mating occurs in the spring, whereby the male grips the female with his jaws and holds onto her by a fold of skin on the neck before copulating.

Like all dragon lizards, Bearded Dragons are egg-layers. In south-eastern New South Wales, females are gravid (with eggs) in mid-spring (around November). On the Eyre Peninsula in South Australia, females lay their eggs in mid-spring. The clutch sizes ranges 11-30 eggs. In captivity, individual females have laid up to four clutches in one "season" (15 October-17 June) at intervals as short as 13 days. There is evidence to suggest that females can store sperm, with records of two clutches being produced from one mating.

The eggs are laid in a burrow dug by the female who then back-fills the entrance to conceal the nest. An excavated nest had a slight deviation approximately two-thirds the distance from the opening and had a slightly rounded egg chamber. Freshly laid eggs vary from 23-29mm in length and 17-18mm in length. Incubation at approximately 26º C took between 78 to 85 days. Hatchlings range in snout-vent length from 39 to 42mm with a mean of 38mm.

Conservation status

Not listed as threatened.

Predators

The known predators of the species include the Gull-billed Tern Gelochelidon nilotica(based on carcasses in tern colonies), goannas, Black-headed Python Aspidites melanocephalus, Dingo, birds of prey as well as introduced carnivores such as cats and foxes.

Central Bearded Dragons are hosts to parasites such as protozoa, nematodes, protozoans, cestodes (round worms) and trematodes (fluke worms).

Management

This species is protected in Australia and cannot be collected from the wild and a permit is required in most states and territories to keep this species in captivity.

Danger to humans

A bite from an adult Central Bearded Dragon can cause pain, break the skin and leave a bruise. Avoiding a bite from this species as not difficult as the lizard will puff, hiss, display and run away before resorting to biting, and only then if it feels physically threatened or severely agitated.

Recent research has indicated that Bearded Dragons poses primitive venom glands, the use of venom in dragon lizards is not yet understood, however a bite from this species should pose no long-term ill effect. The bite site should be cleaned with a mild disinfectant, as with any animal bite.

References

Aland, K. 2008. Dragons, Family Agamidae. From Swan, M. (ed.) 2008. Keeping and Breeding Australian Lizards. Mike Swan Herp Books. Lilydale.

Ehmann, H. 1992. Encyclopaedia of Australian Animals: Reptiles. Angus & Robertson. Pymble.

Fry, B.G. Vidal, N. Norman, J.A. Vonk, F.J. Scheib, H. Ranjan, S.F. Kuruppu, S. Fung, K. Hedges, S.B. Richardson, M.K. Hodgson, W.C. Ignjatovic, V. Summerhayes, R. and Kochva, E. 2006. Early evolution of the venom system in lizards and snakes. Nature 439, 584-588.

Greer, A. E. 1990. The Biology and Evolution of Australian Lizards. Surrey Beatty & Sons.

Further reading

Cogger, H. G. 2000 Reptiles and Amphibians of Australia. Reed New Holland, Sydney.

Swan, G. 1990. A Field Guide To The Snakes and Lizards of New South Wales. Three Sisters. Winmalee.