Across Australia, legal and illegal pet owners are housing exotic animals like ferrets, venomous pit vipers, Indian ringneck parrots, and Burmese pythons.
While many animals bound for the illegal trade are stopped at our borders, there's no reliable data on how many make it through.
A research paper published in the Journal of Applied Ecology this month has found that there are some key attributes that make an exotic pet owner more likely to release an unwanted or unmanageable pet into the wild.
In Australia, it's some of the larger-growing snakes like boa constrictors and Burmese pythons that could fit the bill.
At the same time, birds like Indian ringneck parrots are kept legally, despite being known to cause significant damage to agriculture in their native territory.
Feral pests like cane toads, rabbits, camels, cats, wild pigs and foxes cause hundreds of millions of dollars in damage to agriculture each year, and devastate native wildlife.
So what are the chances that someone's legal, or illegal exotic pet is going to become Australia's next super pest?
Burmese pythons: a warning from the US
According to the United States Geological Survey (USGS), wildlife scientists began noticing fewer medium-sized mammals during surveys of the Florida Everglades in 2003.
Populations of raccoons, bobcats, deer and opossums were plummeting and rabbits disappeared completely.
So scientists released a new population of rabbits fitted with tracking devices into the Everglades.
Within a year, 80 per cent of the rabbits were found in the stomachs of Burmese pythons — a large species of constrictor from South-East Asia that can grow up to 7 metres long in captivity.
By the time the US banned the importation of Burmese pythons for the pet trade in 2012, the population of snakes in the Everglades was out of control, and is now estimated to be in the tens, if not hundreds of thousands.
Burmese pythons, along with common snapping turtles, yellow anacondas and venomous puff adders from Africa are the most likely to establish in Australia if they are released in sufficient numbers, according to a 2016 paper by researchers including Associate Professor Phill Cassey, from the University of Adelaide.
"They would be an environmental disaster and they're [already] here in Australia, no doubt about it."
Research shows large-growing snakes released more often
The latest research, from ecologists at Rutgers University in New Jersey, used 18 years of data from the US reptile and amphibian trade.
They found there were several compounding factors that increased the likelihood of pets being released by their owners.
Not surprisingly, pets that were cheap and that were imported in high quantities were more likely to be released.
But pets that grew to a large size at maturity were also more likely to be set loose.
In Australia's black market, several species of exotic snake tick these boxes, including cobras, boa constrictors and Burmese pythons.
While many are intercepted at our border, plenty are getting through, according to Dr Cassey.
Dr Christy said it's the fast-growing snakes that can become too much for their owners, that are potentially problematic.
"We're concerned about the big snakes like the boas and the Burmese pythons in the illegal trade," she said.
What makes a good pest?
To establish as a pest species in Australia, there are a few hurdles to overcome.
Firstly, the animal or plant needs to get here. Second, it needs to be released into the wild in suitable habitat.
And finally the individual either needs to be pregnant, or be able to find a mate, and build up a viable population.
Most potential pests succumb in these early stages. For instance, a boa constrictor found on the Gold Coast in 2015, is likely to have died before it could find another boa constrictor mate.
Releasing a breeding pair of animals is likely to greatly increase the chances that they can establish.
If an animal can build up a viable breeding population, the enemy release hypothesis — where a species is no longer kept in check by its natural predators — kicks into gear, and any chance of stopping their advance fades.
Fecundity — the ability to produce lots of offspring, and the ability to thrive in a range of habitats, are both attributes that increase an animal's chance of being a successful invader.
In the illegal trade, getting to Australia presents an obstacle that restricts most of our illegal imports to reptiles.
Unlike mammals and larger-bodied animals, reptiles can survive long periods without food and water and when cooled down enter a state of torpor, making them easy to transport, according to Dr Michelle Christy from the Centre for Invasive Species Solutions.
"We had an example of a brown tree snake, that went from Guam to Texas and it was alive at the other end after three months."
'Only a matter of time' before serious pest establishes
The Federal Register of Legislation lists exotic animals that can be kept as pets in Australia, including numerous fish and bird species, and mammals like camels, goats, ferrets, alpaca and guinea pigs.
Although it is supposed to exclude animals that would pose a significant risk of establishing in the wild, some experts have called into question certain animals' legal status.
Indian ringneck parrots, also known as rose-ringed parakeets, are one of the most commonly kept exotic bird species in Australia, and are frequently reported to have escaped.
Several local control measures have been needed to put down fledgling wild populations, and the birds were found to pose an extreme threat of establishing in Western Australia by the Department of Agriculture and Food.
Similarly, while the Queensland Government estimates around 150,000 ferrets are legally kept as pets in Australia, the Queensland and Northern Territory Governments have banned them because of the potential for them to establish.
Since their introduction in the 1800s, ferrets, along with weasels and stoats, have decimated ground-dwelling birds like the kakapo parrot in New Zealand.
Recently established pests in Australia include the smooth newt discovered in Melbourne in 2011, the red fire ant in 2001, and the yellow crazy ant in the 1990s.
But the fact that other invasive species like the Burmese python or Indian ringneck haven't established here in recent years is largely down to luck, according to Dr Cassey.
Like the ferret in New Zealand, at least 1,000 mongooses were introduced to Australia in the 1800s and 1900s to try to control rabbits.
A recent paper found that the likely reason they failed to get a foothold here was that they were introduced to arid areas which were unfavourable mongoose habitat.
Had they been released in favourable habitat, no doubt many more native Australian animals would have succumbed to the "fourth worst invasive mammal in the world", according to the Global Invasive Species Database.
No doubt many of the other exotic pets that have escaped or been released have failed to establish for the same reason.
A Burmese python released in Melbourne or Adelaide may have a slim chance at survival.
But if a breeding pair or pregnant female finds its way to one of our significant wetlands like those along the Murray River or Kakadu, by the time we notice our native species disappearing it may be too late.
By: abc.net.au
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