An Australian study of saltwater crocodiles, inspired by Steve Irwin's legacy, has revealed some surprising facts about these fearsome creatures.
The family business
(From left) Terri Irwin, zoologist Craig Franklin, Robert Irwin and Bindi Irwin in 2012 with “Wenlock”, the 100th crocodile tagged on the Steve Irwin Wildlife Reserve
The saltwater crocodile is a great, stealthy, archaic beast that you wouldn’t expect to pacify with a little friendly tickle on the tail. But here is Daisy, a seven-foot Australian saltie on a grassy shore of the Wenlock River, as placid as a Pekingese. Robert Irwin, the son of the late naturalist Steve Irwin, is stroking the lower third of her thrashing anatomy. Fortunately, a blindfold, gaffer tape and a rope muzzle ensure the amity of this relationship.
Daisy’s sawtooth tail whips the prone boy to the left. “The jaw pressure of the crocodile is incredible—more than 3,000 pounds per square inch!” Robert tells me. Daisy’s tail whips him to the right. “I admire the crocodile’s ability to kill with just its teeth. It’s quite amazing!”
Robert’s older sister Bindi looks on solicitously. Her smile conveys a disarming buoyancy. “Here’s an animal that many people think is just a stupid, evil, ugly monster that kills people. That’s so not true!”
Bindi and Robert are following in the footsteps of their father Steve, the boisterous naturalist of Crocodile Hunter fame. Irwin’s shtick—up-close interactions with dangerous animals and squeals of wonderment (“Crikey!”) at their deadliness—made him a TV phenomenon. Irwin’s encounters ended in 2006 when a stingray’s barb pierced his heart while he was filming on the Great Barrier Reef. He was just 44.
Rethinking the salties
It’s late morning on the Wenlock and the odour of rotten meat hangs in the air. A pig carcass was used to bait the trap that caught Daisy. It was one of 17 traps set along this 30-mile stretch of the river. Bright sun filters down onto the bank, where Robert and Bindi, their mother Terri, and a team of animal wranglers from the family-owned Australia Zoo are taking part in an amazing zoological study.
For more than a decade researchers have monitored the behaviour and physiology of saltwater crocs in Queensland, mainly at the 333,000-acre Steve Irwin Wildlife Reserve, created by the Australian government on the Cape York Peninsula. Their discoveries about the salties’ habits, homing abilities and private lives have prompted a rethink of how they live and how we can co-exist with them. Far from being sedentary, solitary animals with one dominant male defending a set territory, as once thought, salties turn out to be far-ranging creatures with complex social hierarchies.
“Here’s an animal that many people think is just a stupid, evil, ugly monster that kills people. That’s so not true”
The research project is led by Craig Franklin, a University of Queensland zoologist, who has trapped, tagged and released scores of salties. Data is gathered through acoustic telemetry and by satellite transmitters that beam information to a Brisbane lab, which tracks the beasts. The project is bankrolled by the Irwins’ zoo, federal grants and private donors.
Today, a videographer and photographer are on hand to document the work on the Wenlock River for the zoo’s website. While Robert hugs Daisy’s tail, Franklin cuts an incision behind the croc’s left forelimb, inserts a transmitter and wires the wound shut. “The skin is so thick that sewing it together is like trying to stitch up cowboy boots,” says Bindi, a mainstay of Franklin’s annual field trips since day one. Franklin takes blood and tissue samples, and as he measures Daisy, Bindi jots down the figures.
When the blindfolded Daisy lets out a low growl, Bindi flashes a smile. “Crocodiles are very vocal, quite intelligent and so capable of love,” she says. “When an adult female rests her head on her mate’s stomach, there’s no way to describe it but love.”
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Saltwater crocodiles are believed to have the greatest bite force of any living creature
There’s something inscrutable and prehistoric about the crocodile. Some Aboriginal people have traditionally hunted crocodiles for their meat, but their population remained stable until the Second World War ended and high-powered rifles became widely available. Commercial hunters and trigger-happy sportsmen slaughtered them indiscriminately. Since they were given protection in Australia in the early 1970s, their numbers have rebounded, then boomed to about 100,000.
Of the 23 crocodilian species, two inhabit the rivers, billabongs and mangrove swamps of the Australian tropics: the freshwater, or Johnstone’s, crocodile (relatively harmless), and the bigger and far more aggressive estuarine, or saltwater, croc, which can grow to over 20 feet in length and weigh more than a ton. The range of the two overlaps somewhat.
Salties are efficient hunters with nearly 70 interlocking teeth. If one breaks off, there’s another underneath to replace it. Numerous muscles close the brute’s jaws but only a few open them. Over the last 70 million years, not much has changed in the saltie’s evolutionary design. This archosaurian behemoth can see well by day and by night, and has three pairs of eyelids, one of which protects the croc’s vision underwater. A flap at the back of their mouth prevents water from filling the lungs.
Salties stalk their quarry with deadly patience—over days if necessary—learning its habits and feeding times. The croc skulks below the surface near the water’s edge, poised to ambush any of a number of animals, including cattle, wild boar, kangaroos, even other crocodiles as they come to drink. Lunging and chomping, the saltie drags larger prey into deep water where it’s drowned. Executing a death roll, spun by a corkscrew snap of the tail, the crocodile then twists off hunks of meat.
Not for nothing are salties called man-eaters. On average salties attack and eat one person a year in Australia. In 2014, they took three people, with the death of a fourth person most likely the result of a saltie attack.
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Steve Irwin doing what he loved. Image via Femail
What’s perhaps surprising is that Steve Irwin, though controversial for his flamboyant hands-on approach to wildlife, quietly teamed with serious scientists and conservationists to make a real contribution to the systematic natural history of this enigmatic critter.
Irwin wrestled his first crocodile at the age of nine. His father, a plumber who had opened a small reptile park on the Queensland coast, taught him how to catch freshwater crocs, and then how to lug smaller saltwater crocodiles out of the water. Together, they relocated crocs threatened by human settlements to the park.
Irwin took over the business in 1991. The following year he married Terri Raines, a tourist and wildlife rehabilitator from Eugene, Oregon. Footage from their crocodile-trapping honeymoon became the first episode of The Crocodile Hunter.
“They act quite differently without human interference”
As the show grew, Steve and Terri expanded Australia Zoo, with more than 1,200 animals on 100 acres of bushland. Passionate preservationists, Steve and Terri Irwin set up a foundation to protect habitats and wildlife, create rescue programmes and finance scientific research into endangered species. They bought large tracts of land in Australia, hoping to turn them into protected areas, and campaigned against the illegal trade of ivory and exotic furs, and the culling of kangaroos by the Australian government.
In 2003, Franklin met Irwin by chance in Queensland’s Rinyirru National Park. “I was leery of the whole celebrity thing,” Franklin recalls. He was pleasantly surprised. “Despite no formal training, Steve had all the qualities of a great scientist. His intellect was phenomenal, he was driven by curiosity and he had an endless list of questions. His powers of observation proved invaluable in our crocodile-tagging project.”
In 2004, Franklin and Irwin joined forces with the Queensland Parks and Wildlife Service to launch the first published satellite-tracking study. Dozens of adult salties were outfitted with satellite transmitters that record information for a year or more. “The technology lets us access data without disturbing the crocs,” Franklin says. “They act quite differently without human interference.”
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"It’s kind of like seeing an old friend"
Bindi Irwin following in her father's footsteps. Image via Dancing With the Stars
Over the years, researchers have determined that saltwater crocs can hold their breath for nearly seven hours and can dive more than 23 feet; that they’re capable of walking miles between waterholes; that females check out potential nests weeks before laying eggs; that dominant males maximize reproductive success, while subordinates roam hundreds of miles of waterway, possibly in search of unguarded females.
Salties, Bindi points out, invest considerable parental care in the rearing of their young. The female may gently roll eggs in her mouth to assist hatching. When her hatchlings start chirping, she digs them out of the nest, then carries her little darlings to the water’s edge and remains at their side for several months.
What she loves most about the research study is that you can track a crocodile for ten years. Some are caught and recaught and recaught again. Says Bindi, “It’s kind of like seeing an old friend. You become attached to an individual and watch it grow and observe all its changes.”
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