Grey-headed flying fox
Pteropus is primarily an island taxon, with 55 species having some or all of their distribution on islands. Only nine species are found in continental areas (five in Asia and four in Australia), and three (Lyle's flying fox Pteropus lylei, little red flying fox Pteropus scapulatus and the grey-headed flying fox) are restricted to continents. The grey-headed flying fox is very long-lived for a mammal of its size. There are reports[where?] of individuals surviving in captivity for up to 22 years, and a maximum age of up to 15 years seems possible in the wild.
The grey-headed flying fox is the largest bat in Australia. 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 large eyes. The 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. Adult grey-headed flying foxes have an average wingspan of 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 (1.49 lb).
The Australian mainland is home to 75 species of bat. Of these, four species belong to the genus Pteropus: the little red flying fox, Pteropus scapulatus, the spectacled flying-fox, Pteropus conspicillatus, the black flying-fox, Pteropus alecto and the grey-headed flying fox. The grey-headed flying fox is endemic to the south-eastern forested areas of Australia, principally east of the Great Dividing Range. It extends from Finch Hatton in southern Queensland to Geelong, Victoria, where it occupies a more extreme latitude than any other Pteropus species. Recently camps have been observed in Adelaide. Flying foxes are preyed on by eagles, goannas and snakes, as well as crocodiles.
Habitat and movements
Grey-headed flying foxes live 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 the grey-headed flying fox 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 on a variety of foods. Grey-headed flying foxes, along with the three other Australian flying fox species, fulfil 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 and so is of key importance to those forests.
Most vegetation communities that this species forages in 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 who 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. It is in these camps that the flying foxes 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 which contain harems of up to five females. Mating territories are generally 3.5 body lengths along branches. The flying-foxes have neck glands which enlarge in males in the mating season and are used to mark the territories, usually entire branches. Males also defend their territories though aggressive behaviour. The territorial system has been described as similar to a lek system. The males fight to maintain expensive territories, with the most dominant males occupying the centre of the roosting site. The females move from the periphery into the central territories and form into harems. However, the territories may have values other than the males themselves, as they do provide a place for females to roost. Centrally located males are polygamous, while males on the periphery seem to be more monogamous, as they form mixed-sex groups with females that were still nursing their young from the previous year.
Matings are generally observed between March and May but the most likely time of conception is April. Most mating takes place in the territories and during the day. Females have control over the copulation process, and males may have to keep mating with the same females. Females usually give birth to one young each year. Gestation lasts around 27 weeks, and pregnant females give birth between late September and November. Late births into January are sometimes observed. The altrical newborns rely on their mothers for warmth. For their first three weeks, young cling to their mothers when they go foraging. After this, the young remain in the roosts. By January, young are capable of sustained flight, and by February, March or April are fully weaned.
The grey-headed flying fox is now a prominent federal conservation problem in Australia. Early last century the species was considered abundant, with numbers estimated in the many millions. However, in recent years, direct evidence has been accumulating that the species is in serious decline. Current estimates for the species are about 300,000 and it has been suggested that the national population may have declined by over 30% between 1989 and 1999 alone.
Grey-headed flying foxes are exposed to several threatening processes, including loss of foraging and roosting habitat, competition with the black flying fox, and mass die-offs caused by extreme temperature events. When present in urban environments, grey-headed flying foxes are sometimes perceived as a nuisance. Cultivated orchard fruits are also taken, but apparently only at times when other food items are scarce. Because the roosting and foraging habits of the grey-headed flying fox bring the species into conflict with humans, the species suffers from direct killing of animals in orchards and harassment and destruction of roosts. Negative public perception of the species has intensified with the discovery of three recently emerged zoonotic viruses that are potentially fatal to humans: Hendra virus, Australian bat lyssavirus and Menangle virus. However, only Australian bat lyssavirus is known from two isolated cases to be directly transmissible from bats to humans.
Recent research has shown that since 1994, more than 24,500 grey-headed flying foxes have died from extreme heat events alone. This is of increasing concern for the survival of this species now that climate models predict significant increases in the intensity, duration and frequency of such temperature extremes.
To answer some of the growing threats, roost sites have been legally protected since 1986 in New South Wales and since 1994 in Queensland. In 1999 the species was classified as "Vulnerable to extinction" in The Action Plan for Australian Bats, and has since been protected across its range under Australian federal law. As of 2008 the species is listed as "Vulnerable" on the IUCN Red List of Threatened Species.
Bat carers are not only specially trained in techniques to rescue and rehabilitate bats, they are also vaccinated against rabies. Although the chance of contracting the rabies-like Australian bat lyssavirus is extremely small, bat carers are inoculated for their own protection.
Flying foxes often come to the attention of Australian wildlife care and rescue organisations, such as Wildcare Australia, ONARR, Wildlife Carers Darling Downs, Bat Care, Bat Rescue, Tweed Valley Wildlife Carers, WIRES and Wildlife Victoria when reported as injured, sick, orphaned or abandoned. A very high proportion of adult flying fox injuries are caused by entanglement in barbed wire fences or loose, improperly erected fruit tree netting, both of which can result in very serious injuries and a slow, agonising death for the animal if not rescued quickly.
Baby flying foxes usually come into care after having been separated from the mother. Babies are often orphaned during four to six weeks of age when they inadvertently fall off the mother during flight. When they are older, orphans usually come into care because of maternal death from power line electrocution or barbed wire entanglement. A rare, but apparent natural, occurrence of mass abandonment can lead to the rescue of hundreds of babies at one time. The latter most recently occurred in November 2008 at the Canungra bat camp in South East Queensland when Wildcare Australia, working closely with the EPA and regional bat care groups, rescued and rehabilitated over 300 baby grey-headed flying fox. Most babies are in a dehydrated and distressed state by the time they are rescued, and some are infested with maggots if found sick or injured. A young flying fox must be fed every four hours up to six times a day, and then as it develops it is introduced to blossoms and fruit. When the young flying fox is fully weaned around 10 to 12 weeks of age, it goes into a crèche for rehabilitation and eventual release.
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