Feral deer are making a meal of rare and threatened plants in Australia's protected high country, and may also be spreading exotic weeds.
Scientists have analysed poo samples from introduced sambar deer that graze on the Bogong High Plains in the Alpine National Park northeast of Melbourne.
DNA tests show their diet includes imperilled native species but also hawkweed and grey sallow willow - two serious threats to native vegetation that could be hitching a ride with foraging deer to reach new locations.
The research, by James Cook and La Trobe universities, helps plug some of the knowledge gaps about what deer are doing to Australia's rare alpine ecosystems, which occupy just 0.15 per cent of the country.
"Over the last decade, there has been a significant increase in the range and abundance of sambar deer within the Alpine National Park," the study says.
"Although many of the species detected in the diet of sambar deer are considered widespread in the environment, we detected several species of conservation significance."
They included rare wetland plants such as broad-leaf flower rush and the alpine marsh-marigold, as well as snow-patch species including the silky snow-daisy, which is listed as critically endangered in Victoria.
"Although it appears that sambar deer are not selectively targeting these particular dietary items, the extent of browsing may only need to be minimal to have detrimental impacts on rare species," the researchers warn.
They've called for routine monitoring of rare plants to ensure any harmful impacts can be quickly managed.
The Invasive Species Council says sambar deer have bizarre legal status under Victorian legislation, with the once-valued game listed as both protected wildlife and a potentially threatening process.
Conservation officer Peter Jacobs, a former chief ranger for the Alps in Victoria, says it's a baffling situation that must be resolved under the current review of the state's wildlife act.
"It's time the government showed its hand and indicated what they are doing about deer," he said, adding the review was announced about two years ago.
"The wildlife act is there to protect our native wildlife. The bizarre thing is it's also protecting deer, which is a major threat to our native wildlife.
He says there are now up to one million deer across Victoria and they are now a serious environmental pest.
The Victorian government says the review is complex and important and that's why it's taking so long.
"The status of deer as game does not prevent their control when they are causing damage to the environment or property," a spokesperson said, adding $19.25 million has been allocated over four years for the state's deer control program.
Deer plans released by the government include targeted and coordinated approaches to controlling wild deer populations in priority areas of environmental importance.
Earlier this year, Australia's first national plan to manage feral deer was released, warning there was a narrow window to stop the pest invading most of the country.
Australia is currently home to up to two million feral deer, which degrade the land with their hard hooves, spread weeds and disease, graze on native species, wallow in sensitive peatlands, and ring bark young trees.
They are present across a quarter of NSW and Tasmania, and about half of Victoria and half of South Australia's farmlands.
But modelling suggests without more action, most of the country could be inhabited by at least one of Australia's six feral deer species within decades.
The national plan sets out 22 actions designed to stop the westward spread from the east coast where numbers are most concentrated.
