THE troubled Australia Zoo Wildlife Hospital has been branded a "death sentence" by its most loyal animal carers.
Seabird rescuers Paula and Bridgette Powers have vowed never to set foot in the hospital again after a white-faced heron was allegedly euthanised for an old injury. 
The well-known Sunshine Coast sisters - dubbed the Twinnies - have accused staff of mistaking an old broken clavicle for a current fracture.
It comes as another wildlife carer expressed outrage at the euthanisation of a koala with a urinary tract infection.
Paula Powers said the sisters (right) were horrified at the "wrong diagnosis" that led to the bird's death.
She said a vet who undertook a necropsy and offered a second opinion found the heron had no current fractures.
"We were so devastated. They diagnosed her wrong. We said to them: 'We hope you haven't euthanised her; that's an old injury'." The Twinnies' outrage is the latest blow to the zoo, which has been in crisis. Carers fear injured wildlife are being put down because of a lack of knowledge on how to diagnose and treat native animals.
Biosecurity Queensland and the Veterinary Surgeons Board are undertaking separate investigations into allegations of animal mistreatment.
Paula said the sisters had known the white-faced heron since it was treated for a fractured wing and clavicle six years ago.
The heron was released to the wild five years ago but was recently discovered unable to hold her head up and taken to the hospital.
Paula said the sisters had been loyal to the zoo for 17 years, dutifully nursing birds back to health, but would no longer work with them.
"We want the public to bring birds to us and we'll take them to the RSPCA or vet," she said. "We'll never go there (Australia Zoo Wildlife Hos-pital) again. " An Australia Zoo spokeswoman said the hospital was committed to saving lives. "We recognise and appreciate the incredible passion and dedication that we share with all wildlife carers," the spokeswoman said. "Our assessments and decisions are based on veterinary medical expertise and prioritise animal welfare every single time."As can be reasonably expected in any medical -facility, every effort is made to save all patients, however we reiterate the most important thing is the animal's welfare and quality of life."