Land clearing and bushfires are the biggest causes of stress for wild koalas, according to NSW research of stress hormones in faecal samples.
Koala droppings have helped a NSW researcher discover that land clearing is the leading cause of stress for the native marsupial.
The Western Sydney University research suggests land clearing causes more stress for koalas than vehicles, dog attacks and disease.
Bushfires were the second biggest cause of koala stress, the research found.
Report author Edward Narayan assessed the stress hormone levels in faecal samples from nearly 300 koalas across NSW, South Australia and Queensland between 2012 and 2018.
High levels of stress hormones were found in koalas living in areas with land clearance and those living in areas with previous or ongoing habitat changes, the report said.
The research, released on Monday evening, suggests koalas living in these environments could be the most vulnerable to extinction.
"Koalas are facing chronic stress and this can be a significant problem for their survival," Dr Narayan told AAP.
"The demonstrated long-term stress caused by environmental trauma can lead to significant physical and psychological changes in koalas."
These changes can result in an increased risk to infection, suppressed reproduction, growth and high mortality rates, he added.
The senior lecturer hopes his research will further the discussion about the impacts of land clearing and how animals and humans live together.
"Humans have become a bit too greedy and we need to think about the ways we can make animals our priority because if our native species show problems that means our ecosystem is not holding up," Dr Narayan said.
The research was supported by a grant from the International Fund for Animal Welfare, whose regional director Rebecca Keeble called on governments to consider the welfare of animals when planning infrastructure and developments.
"This research proves the true impact of a development on local koala populations remains well after the bulldozers and construction teams have moved on," Ms Keeble said in a statement.
"Koalas must be given more space to live and thrive in if we are going to successfully overcome the challenges posed by urbanisation, human-wildlife conflict and other issues created by human interference."