The Sydney epidemic of 1900-1905 claimed more than 163 lives and was part of a plague pandemic affecting dozens of countries between 1850 and 1912.

In a bid to limit panic and the mounting death toll, the NSW Government offered six pence - four dollars in today's economy - as bounty for the body of every rat delivered to a purpose-built city furnace established in Bathurst Street.

While the eradication campaign was highly successful - more than 100,000 rats were culled during the first six months - it also led to the indiscriminate killing of harmless native rodents, according to UNSW biologists Dr Peter Banks and Dr Grainne Cleary.

"Historical records and photographs suggest that harmless rodents such as water rats and the native bush rats were caught up in the culling of black rats," says Dr Banks.

"Land-clearing for the suburbs of Mosman, Cremorne and Manly then isolated bush patches on harbour foreshores, depriving the native rodents to recolonise bushland habitats. As a consequence, native bush rats have been a rarity in Sydney ever since - the last confirmed sighting in the city was in 1901."

Despite the black rat's fearsome reputation, Dr Banks says early experiments at Taronga Zoo showed that it is "easily bullied" by native bush rats. The team believes that they are likely to "evict" the invaders from bushland when they are reintroduced, with resulting benefits to many other species preyed on by black rats - notably native birds whose eggs are taken.

Beginning next year, the campaign aims to trap 70 per cent of the vermin rats in four areas before releasing bush rats from 2011. If successful, the trial could be expanded to drive the pests out of suburbs across the city.

Provided by University of New South Wales (news : web)