[3] The species shares mainland Australia with three other members of the genus Pteropus: the little red P. scapulatus, spectacled P. conspicillatus, and the black P. alecto.

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.

[5] The grey-headed flying fox is the largest bat in Australia, with the adult wingspan reaching up to 1 m (3 ft 3 in) in length and weighing up to 1 kg (2.2 lb).

The fur on the body is long and streaked with grey, the broad and well defined collar completely encircles the neck with hair that is golden orange in tone.

It relies on smell and, predominately, sight to locate its food (nectar, pollen and native fruits) and thus has relatively large eyes for a bat.

The breeding range has been recorded as progressing southward, the temperate climate of Melbourne and Geelong and no further north than Maryborough, Queensland.

The city of Brisbane has many roosts occupied by the species; a famous colony at the Indooroopilly Island is noted for the evening departure of the bats across the local river.

Within the central business district of Sydney, they can be seen travelling along city streets to feed at Moreton Bay fig trees at Hyde Park.

[10] The species was recorded as an occasional visitor to the national capital Canberra, although the flowering eucalypts at Commonwealth Park have seen more permanent camps established close to the city.

[11] The species was surveyed during the 1920s by Francis Ratcliffe, who recorded the populations in estimates of quarter, half, or one million in camps, generally located around 40 kilometres apart.

[13] These camps are variable in size and are seasonally relocated; the warmer parts of the year find them occupying cool and wet gullies in large groups.

[17] Although recorded in small numbers sporadically throughout the 20th century, it was not until the 1980s that grey-headed flying foxes routinely visited Melbourne,[18] with a permanent camp since the 1990s.

Their residence at the Royal Botanic Gardens Victoria was the subject of controversy, and the bats were eventually discouraged and moved to Yarra Bend at the city's river.

The spread is likely due to global warming, habitat loss and drought; while the location of the new camps appears to be in response to urbanisation: a reliable food supply[20] (such as native eucalypt plantings and backyard fruit trees) and warmer temperatures due to climate change and urban heat islands.

[18][21] As of 2024[update], the bats have been spreading westward, with camps spotted in Port Augusta, on the Eyre Peninsula, and as far north as Katherine in the Northern Territory.

[22] Around dusk, grey-headed flying foxes leave the roost and travel up to 50 km a night to feed on pollen, nectar and fruit.

The grey-headed flying fox is the only mammalian nectarivore and frugivore to occupy substantial areas of subtropical rainforests, so is of key importance to those forests.

The teeth, tongue and palate of the pteropodid bats are able to extract plant juices from food, only swallowing smaller seeds of the meal.

[25] Most of the trees on which this species forages produce nectar and pollen seasonally and are abundant unpredictably, so the flying fox's migration traits cope with this.

The snake species Morelia spilota is frequently found as a resident at these camps, lazily selecting an individual from the apparently unconcerned group at a branch.

[41] The urbanised camps of cities were noted as succumbing to poisoning during the 1970s to 1980s, identified as the lead in petrol that would accumulate on the fur and enter the body when grooming.

An introduced plant, the cocos palm Syagrus romanzoffiana, now banned by some local councils, bears fruit that is toxic to this species and has resulted in their death; the Chinese elm Ulmus parvifolia and privet present this same hazard.

[41][12] The early twentieth century saw the incursion of Pteropus poliocephalus to the opportunities they discovered at orchards, and the government placed a bounty on the declared pest.

[42] Their reputation for destroying fruit crops was noted by John Gould in 1863,[5] though the extent of actual damage was often greatly exaggerated.

When Ratcliffe submitted his report, he noted the number of paid bounties was 300,000, and this would not have included the mortally wounded escapees or those left suspended at roosts by the grip that is held by their weight.

This species continued to be killed or wounded by shotguns, many remaining disabled where they fell after the bounty was stopped, despite the advice of Ratcliffe and later researchers on an ineffective and uneconomical practice and the needless extermination of the population.