The Grey-headed Flying-fox Pteropus poliocephalus has an expansive range. However, the species actually occupies a relatively restricted and continuously changing habitat area, which is primarily defined by irregular patterns of nectar availability. A synchronous count of Greyheaded Flying-foxes in New South Wales taken in July 1988 described the distribution and abundance of the species during a time of general food scarcity, but when abundant floral resources were available in restricted patches of coastal vegetation. The population was highly concentrated into small habitat areas associated with this flowering. The species occupied 11 camps which were located at irregular intervals along the coast, north from the Sydney region. Over 99% of the New South Wales population occurred in nine camps. The total abundance of animals in the state was estimated at 85 400. These results vary substantially from recent estimations which placed the size of the New South Wales population at one million animals. Black Flying-foxes occupied seven camps at the time of the count and their abundance was estimated at 72 500. Periods of concentration are periods of vulnerability for migratory species and present appropriate circumstances in which to examine their conservation status. Critical winter habitat used by Grey-headed Flying-foxes at the time of this study is poorly reserved, primarily occurs on privately-owned land and is located in areas targeted for urban and rural residential development to cater for an ongoing, rapid increase in human population. The conclusion drawn from this study was that Grey-headed Flying-foxes are vulnerable to population decline from the ongoing clearing of their critical over-wintering habitat in lowland coastal vegetation in north-east New South Wales and south-east Oueensland. These results support their listing as VulneraMe in the 1999 Action Plan for Australian Bats.