Christmas Island, sometimes described as the Galapagos Islands of the Indian Ocean for its biodiversity, could be free of feral cats by 2025.
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Until recently, one animal stood in the way of the island's cat eradication program: Christmas Island's own massive robber crabs, also known as coconut crabs.
The crabs are fierce scavengers and were attracted to the bait being used by Parks Australia to draw cats to automated traps, which detected felines and shot them with a poisonous spray the cats then licked off their fur.
Initially, staff were finding the crabs were crushing some of the traps' components to get at the bait, although most were inefficient at accessing it.
In response, staff modified the grooming traps by covering them with retrofitted upside-down wheelie bins fitted with solar panels and a grill over the front of the trap.
The use of 15 such grooming traps contributed a great deal to the culling of 300 cats on the island last year.
There are now an estimated 240 feral felines left and authorities believe they can further reduce the numbers to a few dozen by the end of the year.
A biodiverse wonderland
Christmas Island is one of Australia's most remote territories.
It's located in the Indian Ocean about 1,500 kilometres west of mainland Australia, and is a cornucopia of animal species including endangered birds and reptiles found only on its shores.
About 63 per cent of the island's 135 square kilometres is national park.
Feral cats have already contributed to the extinction of some island species in the wild, such as the blue-tailed skink.
Birds such as the brown booby, which are ground nesters, are also highly at risk.
Parks Australia estimates by removing 300 cats last year, it helped save 10,800 giant geckos, 4,200 threatened birds and more than 380 critically endangered flying foxes.
These figures were based on an analysis of the food found in cat stomachs.
Just one cat was discovered to contain eight half-digested Christmas Island giant geckos.
Parks Australia invasive species manager Derek Ball said last year's eradication effort was an encouraging result for native species recovery.
"I get regular comments from long-term locals on Christmas Island that they're already seeing the improvement in native wildlife on the island," he said.
"People that have been here for a long time, they're constantly saying to us that they're seeing more birds, are seeing more giant geckos, you're seeing more wildlife in general since the eradication campaign started.
"So in 2023, we're ramping up again."
Tough terrain hampers efforts
The landscape of Christmas Island is rugged.
Tall and craggy cliffs abound with thick jungle covering a large portion of the land.
Mr Ball said the terrain made the cat eradication program one of the most complex in the world.
"The Christmas Island terrain is extremely rough," he said.
"We've got some extreme weather conditions to deal with and you know, the team has got a lot of challenges out there in the field."
The few remaining cats could prove the biggest challenge to remove.
Mr Ball said thermal vision drones, environmental DNA detection and biosecurity dogs could be used in the mop-up stage of the program.
Cat containment is key
Federal Environment Minister Tanya Plibersek said the success of the Christmas Island cat eradication program raised hopes for similar outcomes in other parts of Australia.
"Feral cats are one of the worst predators for Australian native animals, they threaten the survival of about 120 nationally listed threatened species," she said.
She commended the grooming-style traps, which use artificial intelligence and can be deployed over a range of landscapes.
Ms Plibersek also said she was supportive of local government efforts to restrict domestic cats to indoors.
"I think most people who own a domestic cat are really responsible. They keep their cat indoors," she said.
"They know that cats are very efficient killers because they've seen the cat bringing the mouse or bring in the rat or bring in the bird.
"It is really important that people keep their cats indoors. That they desex their cats ... [and] that they don't contribute to the wild cat population."
