Boyd's Forest Dragon
|Boyd's Forest Dragon|
|Boyd's Forest Dragon in the Daintree National Park|
Boyd's Forest Dragon (Hypsilurus boydii) is an arboreal agamid lizard found in rainforests and their margins in the Wet Tropics region of northern Queensland, Australia. It is the larger of the two species of Hypsilurus found in Australia. The other species, the Southern Angle-headed Dragon, H. spinipes, is found in southern Queensland and northern New South Wales.
The generic name Hypsilurus comes from 'upsilon-tail'. Upsilon ('ϒ') is the Greek letter on which the English uppercase 'Y' is based. The specific name, boydii, is a reference to John Archibald Boyd, who lived in Fiji from 1865 to 1882 and then on a sugar plantation at Ingham, Queensland, and collected specimens for the Australian Museum and for William John Macleay, who provided the original description of the species.
Distribution and habitat
The species is restricted to rainforests and their margins in northern Queensland, Australia, from just north of Townsville to near Cooktown. It is found in both upland and lowland rainforest, and is often seen around Lake Eacham (Yidyam) and Lake Barrine, and in parts of Malanda Falls Conservation Park and at Mossman Gorge.
It is recorded using tree-hollows.
Boyd's forest dragons are generally brown or grey above, with some individuals having a green flush. The body is laterally compressed. They have very enlarged cheek scales, a prominent nuchal crest, and a yellow dewlap under the chin that is edged with enlarged spines. The tympanum is large and superficial. A dorsal crest, discontinuous with the nuchal crest, consisting of enlarged, hardened and pointed scales, runs down to the base of the tail.
Adults are sexually dimorphic, with males larger than females and having larger, blockier heads. Adult males grow to an average body length (snout-vent length) of about 160 millimetres, with the tail adding another 325 millimetres; average body length for adult females is about 140 millimetres and tail length is about 280 millimetres. Average body mass for adult males is about 150 grams and for females is about 100 grams.
Boyd's forest dragons spend the majority of their time perched on the trunks of trees, usually at around head height, although daily movements can exceed 100 metres on the ground. When approached, they will usually move around to the opposite side of the tree, keeping the trunk between them and their harasser.
Unlike most other lizards, Boyd's forest dragons don't bask in the sun, instead letting their body temperature fluctuate with air temperature (thermoconforming rather than thermoregulating). The one possible exception to this general rule is gravid (pregnant) females, which are often observed sitting on or beside forest roads and exhibit elevated body temperatures.
Boyd's forest dragons typically commence activity at dawn and cease activity at dusk, remaining active even when it rains. Activity is highly seasonal, all but ceasing during the cooler months, when lizards typically move into the rainforest canopy.
Both males and females appear to be territorial, with males defending an area of around 1,000 square metres. Female territories are smaller, with male territories often containing the territories of more than one female.
Hatchlings, juveniles and smaller adults can often be found 'sleeping' at night at the ends of tree branches with their head pointing back towards the trunk.
Boyd's forest dragons are sit-and-wait predators, catching prey that they spy from their perches, although once on the ground, they will frequently move over a wider area, catching prey as they go. Their diet consists primarily of invertebrates, with earthworms making up a relatively high proportion. Small fruits and vertebrates are also occasionally consumed.
Reproduction is via eggs, with clutch sizes varying from one to six eggs. Eggs are about 30 millimetres long and 15 millimetres wide, and weigh about 3-4.5 grams. Egg size and weight are both higher in upland populations. Females in lowland populations may lay more than one clutch in a season, but clutch sizes are typically smaller than those laid by upland females. The eggs are laid in shallow nests, often in rainforest clearings — both natural and man-made (the verges of roads are particularly popular). The eggs take about 100 days to incubate.
Sexual maturity is achieved in around one to two years in lowland populations but probably takes at least a year longer in upland populations.
Small orange mites are commonly found on the dewlap and in the groin areas of the legs.
- Ehmann, Harald (1992). Encyclopedia of Australian Animals: Reptiles. Angus and Robertson.
- Nix, H.; Switzer, M. A. (1991). Rainforest Animals: Atlas of the Vertebrates Endemic to Australia's Wet Tropics. Canberra: Kowari.
- Philip Gibbons, David Lindenmayer (2002). Tree Hollows and Wildlife Conservation in Australia. CSIRO Publishing. p. 9. ISBN 9780643067059.
- Torr, Geordie (1997). "Forest dragons". Nature Australia 25: 32–39.
- Torr, Geordie (2003). "Here be dragons". Australian Geographic 69: 68–77.
- Trembath, Dane; Simon Fearn; Eivind Andreas Baste Undheim (2009). "Natural history of the slaty grey snake (Stegonotus cucullatus) (Serpentes: Colubridae) from tropical north Queensland, Australia". Australian Journal of Zoology 57: 119–124. doi:10.1071/zo08091.
|Wikimedia Commons has media related to Hypsilurus boydii.|