A platypus is released by the CEO of Taronga Zoo Cameron Kerr back into Sydney's Royal National Park for the first time in over fifty years, in Sydney, Australia, on May 12, 2023. (Reuters)

After their mysterious disappearance 50 years ago, platypuses are now returning home to Sydney, Australia, although conservationists remain baffled as to why the egg-laying aquatic mammal vanished from the rivers of Royal National Park.

As part of a collaboration between the University of New South Wales, the National Parks and Wildlife Service, and WWF, 5 or perhaps 6 females were released last week into Hacking River as the first stage of the reintroduction.

The 5 female platypuses came from the Bombala and Dalgety regions and are now being kept at Taronga Zoo’s special platypus refuge.

Australian conservationist with the World Wildlife Fund (WWF), Rob Brewster, stated, “We’ve put females in a week to ten days before the males go in, just to let those girls settle in without those males who are a bit bolder, a bit boisterous,” adding. “Hopefully, those females have found that little niche in their new environment and they can settle in together from there on.”

Brewster said the WWF is expecting to see burrows and territorial establishment near the river banks in the national park from the females before they release the males inside, and that breeding would indicate the success of the reintroduction.

Threat management teams are ensuring that they are not attacked or targeted by foxes or feral cats, and are making sure that water quality is at the highest level for sustainability.

NSW Environment Minister Penny Sharpe expressed, “Royal National Park is Australia’s oldest national park and I am pleased this historic reintroduction will help re-establish a sanctuary for this iconic species".