More than 20,000 hanging around the gardens have caused the death of 18 trees and had damaged more than 300 specimens.

Noise has been used in the past to discourage them from their camp but the Gardens Trust has decided the time has come to move them.

The trust has unveiled to the public its plans to relocate the animals to other parts of Sydney, possibly to locations in St George and Sutherland Shire.

Last Thursday, members of the public were invited to comment on a draft 238-page report about relocation.

Prepared by Melbourne's Royal Botanic Gardens, the plan is based on Melbourne's successful relocation of a similarly sized colony.

Gardens trust executive director Tim Entwisle said flying foxes had to go to spare the area further damage.

"We will not do anything to harm the flying foxes but we have to give relocation a try,'' he said.

Dr Entwisle said it was expected that the animals would go to existing camps around Sydney and that the trust would work with land managers if any new camps were established.

"If these are in unsustainable sites, the flying foxes will be moved on when it is safe to do so,'' he said.

"The flying foxes will be closely monitored to make sure there are no adverse effects on their welfare.''

A year ago, Sutherland Shire Council voted against encouraging extra flying foxes in places such an industrial area in Woolooware Bay, Still Creek near Illawong and Mangrove Island near Como.

Another possible site where the displaced Botanic Gardens flying foxes may find refuge is Wolli Creek where there is already a colony.

A spokesman for RailCorp, which owns the Wolli Creek site where a bat colony lives, said its maintenance and construction work could adversely affect a larger colony and that it was obliged under environmental law to consider such effects.

The flying foxes, also known as fruit bats, are a protected native species listed as "vulnerable'' protected by state and federal government laws.

The State Government approved a licence for the proposed relocation last year.

The Federal Government has advised that the project will have to be assessed through a public environment report dealing with the potential effects of relocation.

The report is open for public comment in writing until

5pm on December 23 and is available at Royal Botanic Gardens Sydney