On a daily basis, they have found several creatures stopped at the sanctuary's predator-proof fence on their way in search of food, water or a mate.
"It just seems to be their natural instinct to migrate at certain times," general manager of the Woodlands and Wetlands Trust Jason Cummings said.
"But the turtles can get stuck at the fence and for whatever reason they don't turn around and go back to where they came from.
"So they will stick there and try to poke their way through but they can't get through."
The Woodlands and Wetlands Trust has also secured $1.2 million in Commonwealth, ACT Government and community funding to help it triple the size of the sanctuary.
The planned expansion would take it from 400 hectares to 1,200 hectares over the next 12 to 18 months.
"It means we can have more bettongs for example and more bush stone curlews," Mr Cummings said.
"But also we can bring other species back, species that are larger and require larger home ranges in a bigger sanctuary."
Mr Cummings said this would make Mulligans Flat the leading sanctuary for the box-gum grassy wetland ecosystem.
He said the group was still looking for donations and would need more volunteers as the fence expanded.
