Hunting platypuses takes patience. On Thursday afternoon, I headed into the Royal national park, south of Sydney, with researchers who had reintroduced a small population of the elusive monotremes two years ago.

There was a big net and torches – and our dinner. It could be a long wait.

The platypus was thought to be locally extinct by the 1970s, after a chemical spill on a nearby highway washed through streams and the Hacking River, devastating the delicate ecosystem that platypuses need to thrive.

But then, in 2023, Dr Gilad Bino, an ecologist and freshwater biologist at the University of New South Wales, and his colleague, Dr Tahneal Hawke, introduced 10 platypuses into the national park in the hope of reestablishing a thriving population.

Dr Tahneal Hawke and Dr Gilad Bino beside the river where they set up 50 metres of netting to ensnare platypuses for research. Photograph: Jessica Hromas/The Guardian

The project paid quick dividends. A newborn platypus was discovered in early 2024 and christened Gilli – a Dharawal word for “flame”. Three more adults were introduced in May.

This week, the researchers were hoping to find evidence that Gilli wasn’t a fluke.

I’ve lived in Australia for 10 years after moving from the US. And like many people, I had never seen a platypus in the wild. So I jumped at the chance to join Bino and Hawke this week when they ventured into the forest in search of their “platys”.

The zigzaggy route

Each platypus introduced to the park in 2023 has a small transmitter about the size of a vitamin tablet. They signal to 40 underwater receivers along the Hacking River, allowing the researchers to know how the platypuses are faring.

A platypus can range over 5km, and they’re “relatively agile”, according to Jackson Wilkes Walburn, a PhD candidate at UNSW working with Bino and Hawke.

The animals can scramble over land, up and down riverbeds and into weirs in search of food, or in the case of the males, mates. That agility can make it hard to know where they might be.

Bino and Hawke set up 50 metres of orange netting on the river on Thursday evening, with floats every metre, so any ensnared platypus could be collected within moments of hearing the telltale “platypus splash”.

Bino unfurls a net to try to catch platypuses in the Hacking River, in the Royal national park. The animals are mostly active at dawn and dusk. Photograph: Jessica Hromas/The Guardian

“Platys often take a bit of the zigzaggy route; they’re not flying down the [river] highway,” Wilkes Walburn says. The long net off the river’s bank gives the team “the best chance of picking them up”.

The animals are crepuscular, meaning they’re mostly active at dawn and dusk. Platypuses feed on spineless waterbugs, worms, yabbies and mayfly larvae, eating for about eight or 10 hours a night. Once the net is in the water, we wait.

A splash in the twilight

When you are new to hunting platypuses, every rustle in the dark sounds like monotreme action. The researchers always have eyes or ears on the net when it’s in the water.

When dusk gives way to darkness, Bino, Hawke and Wilkes Walburn operate as platypus lifeguards, scanning the surface of the net with a spotlight every few minutes. Many research sessions go until midnight, others much later, and Bino and Hawke have been known to pull all-nighters.

At 8.03pm, we hear a splash.

“Right on schedule,” Wilkes Walburn says. He and Hawke jump into a small boat.

A minute later, Hawke has hoisted a platypus out of the net by its tail, checked for venomous spurs (it’s a male – he has them) and placed it into a pillowcase.

Bino is waiting on the riverbank with a scanner to check who has been caught. Each of the released platypuses has an ID chip in the skin folds behind their necks.

Hawke pulls the first catch for the night from the net – a male platypus that was one of the first to be released in the Hacking River in 2023. Photograph: Jessica Hromas/The Guardian

We’ve found Draco. He’s one of the original 10 released in 2023.

“It’s kind of a surprise,” Bino says. Draco is a few kilometres from where the group was released. “We don’t really know where they all are. But it’s great to be reunited with one of the original 10, two and a half years later. Nice!”

Bino still remembers the rush after capturing his first male platypus and reckoning with the spurs. They have a 1 cm-long spur on each hind leg. A prick can cause pain for months. Morphine doesn’t help, Bino says. Thankfully, the trio in the park don’t have first-hand experience.

A bush research theatre

Bino, who was cooking dinner before Draco arrived, races to set up a platypus-sized field hospital. He’ll take a microbiome sample and attach a new transmitter to Draco that should last another three months.

Hawke takes a swab from the mouth of a juvenile platypus that is new to their database. Photograph: Jessica Hromas/The Guardian

The animals are anaesthetised while the tests are being done, something Bino believes is “really important”.

“You draw blood from the tip of the bill; it’s one of the most sensitive organs the animal has,” he says, noting some researchers test lucid animals. “[But] when I started, I was like ‘Uh-uh’.”

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As Bino is with Draco, a call rings out from the riverbank, and platys begin flying into the net. Wilkes Walburn and Hawke have caught another male, but this one doesn’t have an ID chip. It’s a juvenile male, probably about a year-and-a-half to two years old, and just the second young platypus seen in the national park in the past 50 years.

“That’s exciting,” Bino says, turning to Hawke, his research partner for the past 10 years. “Oh, give me a hug! That’s nice, very cool.”

“Unreal!” Hawke says into the night. “Who’s your parent? Gilli’s brother? Cousin? Who knows. So exciting!”

They’ll have to run “everything” with the new platypus: blood tests, urine samples, swabs of the mouth and cheek pouches, a fur sample and a small biopsy. They’ll run a full genome to figure out who his parents are.

The discovery of a juvenile platypus confirms breeding is continuing in the original population introduced to the Hacking River. Photograph: Jessica Hromas/The Guardian

Fifteen minutes later, another platypus comes out of the water. He’s big at 1.6kg, with supple brown fur – another new juvenile. It’s nearly impossible to age older platypuses, but this guy still has a protective sheath around his spurs, which means he was probably born last year and emerged from his mother’s den earlier this season.

The atmosphere is electric in platypus land. Half an hour later, the team catches a fourth platypus of the night. This time it’s a female. They aren’t sure which female, but she is one of a pair released in May in the area.

Death is natural

It’s not always good news, however. Earlier this month, a kayaker found a dead platypus in the Royal national park. It was a male named Chaos from the original cohort of 10. Tests are ongoing to find out the cause of its death.

“Life and death is natural,” Bino says. “It could be natural mortality. We introduce adults and they have a natural longevity. [But] it’s a rough period for males.”

It’s peak mating season for platypuses and males can exhaust their energy stores while looking for a partner – or during territorial fights with other males.

“We’re very sad to be aware of this [loss]. But the survival has been great, they’re breeding, the reintroduction is currently successful,” Bino says. Platypuses can live up to 20 years in the wild, according to the Australian Museum.

There have been pollution scares. Peabody Energy, the operator of a coalmine upstream from the Royal national park, was issued with a clean-up notice after a landslip turned the waters of some streams feeding into the Hacking River an oily-black. The event was localised and didn’t have any major negative effects on the program.

Peabody has since become a major funder of Bino’s research, via a three-year $630,000 grant to support the next phase of the relocation project after funding from the NSW government and the WWF ran out.

“I’m not stupid, but they’re a significant stakeholder in the catchment. So I see that as value,” Bino says of the energy company. “If they’re polluting, I’ll say they’re polluting, but it’s important to involve industry.”

Peabody Energy says it’s “proud to support the dedicated UNSW research team working to return an iconic species to its natural home”. “The encouraging results show real progress toward a self-sustaining platypus population,” a spokesperson says.

Hawke and Bino examine the foot of a juvenile male. Photograph: Jessica Hromas/The GuardianA good night anywhere

Yuin elder Uncle Dean Kelly, who named Gilli, says the discovery of two more juveniles on Thursday is an important moment for the park – and for the species.

“It’s a successful thing that’s happened now with the platypuses, the relocating and now having the next generation,” Kelly says.

“We know it can work, and there should be support … to continue. We know the platypus is an old animal, an ancient animal. That’s the plan, to continue to work with guys like Gilad [Bino] and … make sure these species survive for generations to come.”

Bino, Hawke and Wilkes Walburn pull out the net at midnight and get ready to release the quartet of captured platypuses.

One at a time, the monotremes are taken to the riverbank, their pillowcases opened up, before they make a dash to the safety of the water.

“Four platypuses. In the Royal. That’s a good night anywhere,” Hawke says.