Jerry Olsen, who has studied birds of prey for 40 years, says the eagles eat lots of echidnas, and species of bandicoots which people believed no longer existed in the ACT region.

''There's been interest in bandicoots in the ACT because they are extinct - our wedge-taileds caught three of them.''

An inspection of animal remains in peregrine falcons' nests revealed eight species of animals not supposed to be in this region, including a long-tailed jaeger, an arctic bird.

Mr Olsen said he'd discussed this with rangers following evidence in nests of birds feeding on bandicoots at Rob Roy Range Nature Reserve at Tuggeranong.

Mr Olsen said myths surrounded wedge-tailed eagles, but their ability to bring down a good-sized kangaroo was true.

A carpenter working at his place had watched them from his cabin at Angle Crossing on the Murrumbidgee River killing kangaroos. Rangers had seen them killing kangaroos. Mr Olsen, a member of the Institute for Applied Ecology at the University of Canberra, said adult eagles paired up to harass and hit kangaroos in the back of the head, trying to kill them.

''The rangers have seen this more than we have. They give me two stories. One is, the eagles bang these reasonable-size female kangaroos in the head until they eventually knock them down and subdue them.

''A ranger has also told me they hit kangaroos in the legs and sort of flip them over.''

Eagles were not coping with Canberra's urban sprawl. Mr Olsen does field work in raptor biology, particularly raptor reproduction and ecology and advises local governments on conservation in natural and urban settings. He said the national arboretum and new suburbs in Molonglo were driving wedged-tailed eagles away.

''The arboretum might seem like good news and might seem like it's helping the natural world but it has displaced a pair of eagles that were there for at least 30 years.''

Poison is also depleting eagles. Mr Olsen said poison killed a female wedged-tail nesting at Mount Wanniassa about 2003.

''We watched her for a while and she became weaker and weaker. Finally, she was trying to incubate eggs, she died on the eggs.''

Another young female waited for the older bird to die and had taken over the nesting site.

Wedge-tailed eagles feed on rabbits, but an explosion in rabbit numbers across the territory was not influencing their numbers, Mr Olsen said.

''They seem to be decreasing as rabbit numbers increase. There's your paradox.''