The grey-headed flying fox is endemic to the south-eastern forested areas of Australia, principally east of the Great Dividing Range. Its range extends approximately from Bundaberg in Queensland to Geelong in Victoria, with outlying colonies in Ingham and Finch Hatton in the north, and in Adelaide in the south. In the southern parts of its range it occupies more extreme latitudes than any other Pteropus species.
The grey-headed flying fox is the largest bat in Australia. This flying fox has a dark-grey body with a light-grey head and a reddish-brown neck collar of fur. It is unique among bats of the genus Pteropus in that fur on the legs extends all the way to the ankle. Adults have an average wingspan up to 1 m (3.3 ft) and can weigh up to 1 kg (2.2 lb). The head and body length is between 230 and 289 mm (9.1 and 11.4 in), with an average of 253 mm (10.0 in). The forearm length is between 138 and 180 mm (5.4 and 7.1 in), with an average of 161 mm. Weight generally varies between 600 and 1,000 g (1.3 and 2.2 lb), with an average of 677 g (1.493 lb). It is tailless, with claws on its first and second digits. Since it does not echolocate, it lacks tragus or leaf ornamentation found in most species of Microchiroptera. It relies on sight to locate its food (nectar, pollen and native fruits) and thus has relatively large eyes for a bat.
The grey-headed flying fox is long-lived for a mammal of its size. Individuals reportedly survived in captivity for up to 23 years, and a maximum age of up to 15 years seems possible in the wild.
Grey-headed flying foxes live in a variety of habitats, including rainforests, woodlands, and swamps. During the day, individuals reside in large roosts (colonies or 'camps') consisting of hundreds to tens of thousands of individuals. Colonies are formed in seemingly arbitrary locations. Roost vegetation includes rainforest patches, stands of melaleuca, mangroves, and riparian vegetation, but roosts also occupy highly modified vegetation in urban areas. A prominent example existed for many years at the Royal Botanic Gardens in Sydney. However, the Garden instituted a controversial policy to remove them from the garden grounds. The camp is now dispersed across Queensland.
Movements of grey-headed flying foxes are influenced by the availability of food. Their population is very fluid, as they move in response to the irregular blossoming of certain plant species. They are keystone pollinators and seed disperses over 100 species of native trees and plants. The grey-headed flying fox is a partial migrant that uses winds to facilitate long-distance movement. It does not migrate in a specific direction, but rather in the direction that will be the most beneficial at the time.