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 P. scapulatus, spectacled P. conspicillatus, and the black P. alecto. The grey-headed flying fox is the largest bat in Australia.
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.
As of 2021, the species is listed as "vulnerable" on the IUCN Red List of Threatened Species and Australian Government's Environment Protection and Biodiversity Conservation Act threatened species list.
Taxonomy A description of the species was published by Coenraad Temminck in his 1825 monograph of mammals. Hybridisation with the species Pteropus alecto has been noted where their ranges intersect.
The common names for Pteropus poliocephalus include grey-headed kalong. The entry in Gould's Mammals of Australia (1863) gave the bat the title grey-headed vampire.
Description
The grey-headed flying fox is the largest bat in Australia, with the adult wingspan reaching up to in length and weighing up to . Weight generally varies between , with an average of . The combined length of the head and body is from 230 to 290 mm. The forearm length is a range from 138 to 180 mm. The length of the ear from the tip to base is 30 to 37 mm.
The overall colour of the pelage is a dark-grey body with a light-grey head, separated by a reddish-brown collar. 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. A unique characteristic among bats of the genus Pteropus is fur on the legs that extends all the way to the ankle.
Like many megachiropterans, the species lacks a tail. All of these bats possess claws on its first and second digits. The head is simple in form, with the characteristic 'dog-like' appearance of the genus. Since it does not echolocate, it lacks the tragus or leaf ornamentation found in many species of Microchiroptera. 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 voice of P. poliocephalus consists of a complex series of squeals and screechings. They will flap their wings in hot weather, using blood pumped through the patagium to cool the body temperature.
The grey-headed flying fox is long-lived for a mammal of its size. One study found that in the wild individuals live on average 7.1 years and can live as long as 18 years. In captivity, one specimen has been observed living 23 years.
Grey-headed flying foxes have been found to experience torpor.
Ecology Distribution The distribution range is at the eastern regions of the Australian continent, mostly within 200 kilometres of the coast, from Gladstone in Queensland through to the southern Gippsland region and populations around the city of Melbourne. The breeding range has been recorded as progressing southward, the temperate climate of Melbourne and Geelong and no further north than Maryborough, Queensland.
Urbanisation may displace the species, or provide habitat that accommodates their feeding or roosting preferences. 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. 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.
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. These numbers have greatly declined since this first survey.
Habitat and movements
Grey-headed flying foxes live in a variety of habitats, including rainforests, woodlands, and swamps. 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. 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 botanic gardens 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 dispersers of over 100 species of native trees and plants."L Pope 2014" / Some Touch of Pity, pub=sid harta The grey-headed flying fox is a partial migrant that uses winds to facilitate long-distance movement. It does not migrate in a constant direction, but rather in the direction that will be the most beneficial at the time.
Although recorded in small numbers sporadically throughout the 20th century, it was not until the 1980s that grey-headed flying foxes routinely visited Melbourne, 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 camp at this site was decimated during a heat wave, requiring its rehabilitation to sustain the relocated population. The forced relocations are also said to have led to the discovery of the orchards of the Goulburn Valley. Similarly, the first recorded permanent camp in Adelaide was established in 2010. 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 (such as native eucalypt plantings and backyard fruit trees) and warmer temperatures due to climate change and urban heat islands.
, the bats have been spreading westward, with camps spotted in Port Augusta, on the Eyre Peninsula.
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. These include eucalypt, particularly Corymbia gummifera, Eucalyptus muelleriana, E. globoidea and E. botryoides, and fruits from a wide range of rainforest trees, including members of the genus Ficus. 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.
The teeth, tongue and palate of the pteropodid bats are able to extract plant juices from food, only swallowing smaller seeds of the meal. Incisors hold items such as fruit, and the fibrous material is ejected from the mouth after it is masticated and the juice is swallowed; larger seeds may be held in the mouth and dispersed several kilometres from the tree. The need for the elaborate intestinal tract of most herbivores is consequently removed. Some fruiting plants produce food for flying-foxes, and P. poliocephalus is attracted to the scent of their flowers and fruit and is able to locate the pale colour that indicates the source; the fruit and blooms of species that attract birds in the daylight are usually contrasting reds and purples. The food source is also presented away from the foliage that may obstruct the bat's access.
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 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 and wait until all their females have left. The flying foxes that leave the roost earlier are more vulnerable to predation, and some flying foxes will wait for others to leave, a phenomenon labelled the "after you" effect.
Social organisation 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.Welbergen, J.A. (2005) "The social organisation of the grey-headed flying-fox". PhD thesis, University of Cambridge, Cambridge. 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. Centrally located males are polygamous, while males on the periphery are monogamous or single. The mating system of the grey-headed flying fox is best described as a lek because males do not provide any essential resources to females and are chosen on the basis of their physical location within the roost, which correlates with male quality.
Reproduction