Frilled-Neck Lizard

When startled, the frilled-neck lizard first tries a bluff, then bolts. It rears up on its hind legs and runs bipedally, often with its frill still open, and keeps going until it reaches the nearest tree. Climbing is its main escape: it spends more than 90 percent of each day in trees, mostly resting on trunks and low branches, and comes down mainly to feed. It prefers fleeing to fighting. Before running, it may hiss, lunge, or chase the predator. If running is not an option, it may freeze motionless or hide under low vegetation. Its predators include birds of prey, larger lizards, snakes, dingoes, and feral cats. In the dry season, lizards favor large trees with canopy perches, while in the wet season they prefer shorter, smaller-diameter trees where activity is higher.

When alarmed, a frilled-neck lizard opens its brightly colored pink or yellow mouth and raises its frill, a pleated disc of skin that spans about 30 cm (12 in) when fully extended, more than four times the length of its torso. The display comes with puffing, hissing, and tail lashing, and the lizard may stand on its hind legs, lunge, or chase. Frill color varies by region: red west of the Ord River, orange between the Ord River and the Carpentarian Gap, yellow to white farther east, and yellow in New Guinea. Males are larger and have proportionally bigger frills, heads, and jaws. If the bluff fails, the lizard can bite with large canine teeth, though it generally prefers to flee. Hatchlings are born with proportionally smaller frills than adults.

Frilled-neck lizards depend heavily on camouflage. Their backs range from grey and brown to orangish-brown and black, the underside is paler, and the tail is obscurely striped with a dark tip. They are diurnal and spend more than 90 percent of each day in trees, resting on trunks and low branches, so they are usually noticed only when they descend after rain or to forage. On the ground they take mainly invertebrates such as termites, ants, and centipedes, with termites most important in the dry season and moth larvae in the wet season. They prefer elevated, well-drained ground with eucalypts and avoid lower plains with paperbarks (Melaleuca) and pandans. Activity is lower in the dry season, when they favor large trees with canopy perches, and higher in the wet season.

Frilled-neck lizards are diurnal, largely solitary except during breeding, and males defend territories. Territories lie in savannas and woodlands from the Kimberley to Cape York, and home ranges are small. At Kakadu, males use about 1.96 ha (4.8 acres) in the dry season and 2.53 ha (6.3 acres) in the wet season, while females use 0.63 to 0.68 ha (1.6 to 1.7 acres). Males also travel farther each day, averaging 69 m (75 yd) compared with 23 m (25 yd) for females. Territorial disputes involve frill displays, and fights include pouncing and biting at the rival’s head. Males are the larger sex: one study lists adult males at about 290 mm (11.4 in) snout to vent and at least 870 g (1.9 lb), against 235 mm (9.3 in) and 400 g (0.9 lb) for females.

Breeding runs through the wet season, from about October or November to February or March, though another source places it in the late dry and early wet seasons. Males use frill displays to attract mates and to challenge rivals, but one source says there is no conclusive evidence that mate selection depends on frill size. Lizards reach sexual maturity within two years. Sex is temperature dependent: milder nest temperatures produce more males, while more extreme temperatures produce more females. Females dig a shallow nest cavity, often in flat, coarse-grained sandy soil with sparse grass and leaf litter and no vegetation directly overhead. Clutches can reach 8 to 23 eggs, and eggs hatch in about 70 days by one account and two to four months by another. Hatchlings are independent from birth.

Frilled-neck lizards give no parental care. Females lay their eggs in an underground nest. Hatchlings weigh only 3 to 5 g (0.1 to 0.2 oz) and emerge ready to fend for themselves. Their frills are proportionally smaller than those of adults. Clutch sizes range from 4 to more than 20 eggs, and a female may produce two clutches in one season. Captive lizards average 9.9 years, and some have lived to 20. Wild lifespan is unknown, so figures come from captives. One source gives lifespans of up to six years for males and four years for females. Habitat loss and predation, especially by feral cats, affect some areas, and the pet trade is another threat. Cane toads do not appear to affect them significantly. In New Guinea, the species occurs in the Trans-Fly region.