The grey-headed flying fox (Pteropus poliocephalus) is a megabat native to Australia. The species shares mainland Australia with three other members of the genus Pteropus: the little red flying fox (P. scapulatus), the spectacled flying fox (P. conspicillatus), and the black flying fox (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 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.
Habitat and movements
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 at the Royal Botanic Gardens in Sydney. However, the Garden instituted a successful 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. 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.
Diet and foraging
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 species consumes fruit flowers and pollens of around 187 plant species. Theses include Eucalyptus, particularly Eucalyptus gummifera, Eucalyptus muellerana, Eucalyptus globoidea and Eucalyptus botryoides, and fruits from a wide range of rainforest trees, including members of the Ficus genus. These bats are considered sequential specialists, since they feed on a variety of foods. Grey-headed flying foxes, along with the three other Australian flying fox species, fulfill a very important ecological role by dispersing the pollen and seeds of a wide range of native Australian plants. 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.
Most vegetation communities 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 time when flying foxes leave their roosts to feed depends on foraging light and predation risk. Flying foxes have more time and light when foraging if they leave their roosts early in the day. The entire colony may leave later if a predatory bird is present, while lactating females leave earlier. With males, the bachelors leave earlier than harem-holding males, which guard their wait until all their females have left. The flying foxes that leave the roost earlier are more vulnerable to predation, and some other flying foxes will wait for others to leave, a phenomenon labelled the “after you” effect.
Groupings and territories
Grey-headed flying foxes form two different roosting camps, summer camps and winter camps. Summer camps are used from September to April or June. In these camps, they establish territories, mate, and reproduce. Winter camps are used from April to September. The sexes are separated in winter camps and most behaviour is characterised by mutual grooming. Summer camps are considered “main camps”, while winter camps are referred to as “transit camps”.
In their summer camps, starting in January, male grey-headed flying foxes set up mating territories. Mating territories are generally 3.5 body lengths along branches. These flying foxes’ neck glands enlarge in males in the mating season, and are used to mark the territories. The males fight to maintain their territories, and this is associated with a steep drop in the males’ body condition during this time. Around the beginning of the mating season, adult females move from the periphery towards the central male territories where they become part of short-term ‘harems’ that consist of a male and an unstable group of up to five females.