Australian Water Dragon

The Water Dragon is Australia's largest dragon lizard and can be found living along healthy waterways in Sydney.

Identification

The genus Physignathus was described by George Cuvier (1769-1832) in 1829 based on the type specimen of the genus; the Green Water Dragon, Physignathus cocincinus of south-east Asia. The name Physignathus translates to "puff-cheek" and refers to the bulging appearance of the throat and lower jaw. Physignathus comprises two recognised species; Physignathus lesueurii and Physignathus concincinus. The specific name lesueurii honours the French naturalist Charles-Alexandre Lesueur (1778-1846) who collected this species on the Baudin expedition of 1800. There are two recognised subspecies of Water Dragon; the Eastern Water Dragon, Physignathus lesueurii lesueurii and the Gippsland Water Dragon, Physignathus lesueurii howittii. A recent taxonomic review concluded that the Australian species of Physignathus shows enough differing characteristics to classify it in its own genus, since Physignathus was first assigned to P. cocincinus, a new genus hand to be created for the Australian Water Dragons. In 2012 the species was officially renamed Intellagama lesueurii.

The Water Dragon can be identified by a distinctively deep angular head and nuchal crest of spinose scales that joins the vertebral crest extending down the length of its body to the tail. Enlarged spinose scales are also present across the lateral surface, unevenly distributed amongst regular keeled scales. The jowls are large and ear is exposed and of almost equal size of the eye. The dorsal ridge and tail are laterally compressed and the limbs are strong and robust with particularly long toes on the hind legs. The tail is capable of regeneration when lost, furthermore, regenerated tails can also grow back when severed.

Colouration differs between the subspecies; the Eastern Water Dragon, Intellagama lesueurii lesueurii, has a grey to brownish-grey colour above with patterns of black stripes along the dorsal ridge as well as down the tail. There is also a dark stripe horizontally from the eye back over the tympanum and extending down the neck. The limbs are mostly black with spots and stripes of grey and the tail is patterned with grey and black stripes. The ventral surface is yellowish-brown, with the chest and upper belly becoming bright red in mature males.

The Gippsland Water Dragon, Intellagama lesueurii howittii, is identical in morphology apart from slightly smaller spinose scales but differs in colouration and patterning. Dorsally the body is olive-green to brown in colour with transverse black stripes. The dark stripe from the eye to ear is absent. Mature males have dark blue-green chests and streaks of yellow and blue around the neck and throat.

Habitat

The habitats available to this species differ greatly over its distribution, from tropical rainforest in the north to alpine streams in the south. Flowing water with ample tree cover and basking sites appear to be the key to habitat preference for this species. Water dragons will be found in built-up urban areas provided that the above conditions can be found and water quality is fair.

Distribution

Water Dragons are found in eastern Australia as well as southern New Guinea. The Eastern subspecies, Intellagama lesueurii lesueurii, occurs along the east coast of Australia from Cooktown in the north down to the New South Wales south coast (approximately at Kangaroo Valley) where it is replaced with the Gippsland subspecies Intellagama lesueurii howittii, which is distributed as far south and into the Gippsland region of eastern Victoria. There are also at least one anthropologically introduced feral population found in the Mount Lofty Ranges near Adelaide in South Australia.

Seasonality

Water Dragons are usually active in the Sydney region from September to June, becoming inactive during the cooler months. To survive the the low winter temperatures Water Dragons will enter established burrows or scrape their own between boulders and logs in or near riverbanks and pack dirt into the opening to seal themselves off. Once entombed they will slow their metabolism and enter a state of brumation until spring arrives.

Feeding and diet

Water Dragons are completely insectivorous as juveniles, however as they grow they become more omnivorous with vegetable matter gradually making up to almost half of the diet. In the wild Water Dragons have been observed ground feeding on insects such as ants as well as foraging amongst the branches of trees for arboreal invertebrates like cicadas. They may also consume molluscs and crustaceans such as yabbies, and individuals have been reported foraging for algae and crabs in intertidal zones of the Sydney region. Juvenile Water Dragons have also been observed feeding on mosquitoes which they will jump in the air to catch. Types of vegetation reportedly consumed include figs, lilly-pilly fruits, and other fruits and flowers. Water Dragons are believed to forage underwater, however this is based on one observation of diving Water Dragons returning to the surface and moving their jaws.

Other behaviours and adaptations

The Water Dragon is more often heard than seen as it dives into the water when disturbed. It can remain submerged for around one hour. This species has a much lower preferred body temperature than other large dragons and can remain in the water or in shade on hot days. They are often seen on overcast days or in the morning basking in the available heat.

Water Dragons have quite contrasting activity patterns that are dependent on the season and average daily temperature within its range. During spring and summer, Water Dragons of all ages and sizes can be seen in the various riparian environments they inhabit - basking on riverbanks and rocks, lounging in trees, swimming, as well as foraging for food on land. They can sometimes be hard to observe, and even animals accustomed to human attention will be quick to escape if approached too closely, by either dropping from rock ledges and branches into the water or running bipedally to the water or thick cover. Young Water Dragons prefer to be on the ground and appear to be more wary than the larger adults. Juveniles of I. l. lesueurii have been observed staying completely still when discovered in a grassed section metres from the water, relying heavily on their dull grey camouflage to blend in with the grass and fallen leaves.

Communication

In the wild, Water Dragons can be found in large numbers in areas of suitable habitat. These groups are usually comprised of several females, juveniles of various ages and a dominant male who will defend as much of the territory as possible from other males. Water Dragons communicate through a variety of dominant and submissive signals including head-bobbing, saluting and substrate licking. The actual meaning of some of these displays is not yet fully understood.

Life history cycle

Growth rate is fastest in the first year with hatchings from one mark-recapture project growing 2.25mm or 1.25g per month. One individual measured in its first season in March 1990 was 78mm from snout to vent and weighed 17g. The following year in January this same individual had a snout to vent length of 101mm and was 34g.

Breeding behaviours

The timing of breeding is determined by the onset of warmer weather in spring which occurs sooner in populations inhabiting northern Queensland and later in populations living in Gippsland. In the Sydney region, the breeding season begins in September, when courtship and mating begins, and concludes in January when the last clutches of eggs are laid.

Males are thought to be sexually mature at a snout-vent length of about 210 mm and a mass of 400 g. In the wild this occurs at approximately 5 years of age; in captivity however this can occur as early as 2 years. A single captive female was recorded reproducing from the age of 4 until it was 27 years of age. It is unclear how long males can remain reproductive.

Males of similar size will fight each other when confronted. A male will first attempt to deter his opponent through intimidation, e.g. by walking tall and puffing out the throat with the mouth open wide (see Image 18), and will try to appear as large as possible. If this does not deter the opponent, then ritual combat will result. Male combat includes both animals siding up to each other on the ground so that each animal has its head next to its opponent’s hip area. Both animals will circle each other while taking short bites at each others hip and neck regions. Then they may stop still before erupting into action and repeating this pattern over several more times. Before the end of the battle both opponents will have wounds from biting and scratching on their hips and necks. Fighting between wild males has been observed lasting for ten minutes.

Females can reproduce twice a season in captivity; however this has not been reported in mark-recapture studies of wild populations.

Females begin digging test holes in sandy soil from a week to three days prior to laying. Water Dragon clutch size ranges from 6 to 18. Mean mass of individual eggs varies from about 4.0 to 5.1g.

Conservation status

Protected in all states and territories where it occurs naturally: Queensland, New South Wales, Australian Capital Territory and Victoria. Not listed as threatened in any state or territory.

Predators

Small Water Dragons have been observed being taken by Brown Tree Snakes Boiga irregularis which hunt for them in the tree branches as they sleep. Other species of snakes known to prey on juvenile Water Dragons include Death Adders Acanthophis antarcticus, Copperheads Austrelaps superbus and Red-bellied Black Snakes Pseudechis porphyriacus. Hatchlings and young dragons are also known to be cannibalised by adult Water Dragons in some wild populations.

Management

This species is protected in Australia. Wild specimens cannot be collected from the wild and a permit is required in most states and territories to keep this species in captivity. Please see the Animal Keeping Resources page on the Live Exhibits section and check with your local wildlife licensing agency.

Danger to humans

Large adult Water Dragons will appear confident and friendly however they should not be approached as they have very sharp claws and can deliver a serious bite.

Fossils description

Fossils belonging to the genus Physignathus and resembling extant Water Dragons have been discovered in Miocene deposits in Riversleigh, Queensland, indicating that this genus has existed in Australia for at least 20 million years.