Australia's revegetation efforts are insufficient to sustain remnant populations of small woodland birds. A Greening Australia program that aims to return birds to the landscape recognises that, to reoccupy an area, birds need a minimum of 10 to 20 hectares of native vegetation with a dense understorey, and perhaps 100 hectares to settle and breed. Birds are useful bioindicators and they provide free pest control for woodland trees. The rebirding program is a step towards evolving Australian agriculture away from the alien system brought from the Northern Hemisphere.