Australian Geographic – July-August 2019

42 Australian Geographic

I

T’S MOSTLY BLUFFand bluster, but a frillneck lizard’s

display when it’s disturbed can still be surprisingly intim-

idating. Open-mouthed, with its dinner plate-sized,

bright-red frill erected around its neck like a scaly umbrella,

a ‘frilly’ lunges and hisses at biologist Christian Alessandro

Perez-Martinez at Fogg Dam Conservation Reserve, on the

Adelaide and Mary river f loodplains in the Northern Territory.

Between lunges, it sways back and forth and makes loud

cracking sounds by whipping its tail. Eventually, it turns and

scampers off on its hind limbs to scramble up the nearest tree.

“This dramatic performance aims to deter predators, or at least

momentarily overwhelm them, so that the frillies can escape,”

Christian says. “Even though frillies aren’t dangerous to humans,

their behaviour definitely makes you think twice.”

Christian is a visiting researcher in The Lizard Lab at Macquarie

University, Sydney, where he’s been working in collaboration

with Associate Professor Martin Whiting. He’s been carrying

out some of the first field research on these enigmatic lizards,

which are common across the tropical savannah and woodlands

of northern Australia and New Guinea. Although an adult male

here is rarely bigger than 75cm in length and 750g in weight,

collecting the data Christian needed on the lizards’ colour and

anatomy was more difficult than he expected it to be.

“The frillies would constantly lock eyes with me and frill

up, and on several occasions managed to get a good tail-whip

to my face,” he says.

Christian’s work has involved finding frillnecks asleep at

night in eucalypt canopies. During 120 days in late 2017 and

early 2018, he carefully captured 53 animals to run behavioural

trials in an enclosure, where he recorded the lizards’ responses

to models of predators, hoping to figure out, once and for all,

precisely how their display works.

I

T MAY SEEM obvious that the display is to scare predators,

but until Christian’s study, no-one had properly investigated

how it works in the wild. Indeed, when scientists first turned

their attentions to frillneck behaviour about three decades ago

there were many outlandish suggestions about the frill’s purpose.

“[It’s] the largest and most dramatic display structure seen in

any reptile,” says University of Sydney reptile expert Professor

Rick Shine, who was the first to conduct a detailed field study

of frillneck ecology and behaviour. In the mid-1980s, he spent

300 hours observing the species in Kakadu National Park, east

of Darwin (see AG 28). Before that, there wasn’t a single scientific

paper on frillneck biology, although there were many colourful

explanations for the frill’s purpose.

“Different theories on the evolution of the frill have been

thrown around for decades,” Christian explains. “It was initially

hypothesised that the frill might be used by lizards to parachute

down from the canopy, but this theory and others, such as a role

in thermoregulation [body temperature control], don’t appear to

hold true.”

This paler lizard is from Broome

in northern WA. Diet and genetics

may a

ect colour variations

across the species’ range.

• PHOTO CREDITS, PREVIOUS PAGE: CHRISTIAN ALESSANDRO PEREZ-MARTINEZ; THIS PAGE: JASMINE VINK