An unpublished government report on feral deer shows Australia is failing in its efforts to stop the spread of what one advocate warns could become “Australia’s next feral pig ”.

The five years from 2020-2025 over which the national feral deer action plan was assessed covers a period in which the famously elusive species has increasingly encroached upon major cities, leading to more frequent encounters – including a memorable occasion in which two men in various degrees of undress were fined after becoming lost in the bush when they were spooked by deer while nude sunbathing .

The report says deer, one of the country’s “most rapidly increasing invasive pests”, have both increased in numbers and spread in territory, costing more than $91m in production loss and management time every year.

Deakin University’s Prof Euan Ritchie, president of the Australian Mammal Society, said he was “not at all” surprised by this year’s national vertebrate pest management report card.

“This report shows that governments…