Grey-headed Flying Foxes in the Wolli Creek Valley

Grey-headed Flying foxes in the Wolli Valley - Andrew Smith

This article was written by Andrew Smith. Andrew is an Honours student completing a thesis on flying foxes and has recently visited the Wolli population to count & photograph them.

For the first time that we know of, Grey-headed Flying Foxes (Pteropus poliocephalus) have been noticed roosting in the Wolli Creek Valley. It is possible that they have camped here before as this species often chooses historical roost sites that have been used on previous occasions. Due to their nocturnal nature, flying foxes and other bats generally go unseen. There appears to be a general perception that bats are unclean and dangerous but this notion is misguided. People who visit the Botanic Gardens see thousands of flying foxes and believe that these animals are abundant. This is another misconception. It is truly important for Australians to understand the vital role flying foxes carry out in maintaining the continued health of forests on the east coast of Australia.

Grey-headed flying foxes roosting

Bats are warm-blooded mammals just like us and the Grey-headed Flying fox is one of the largest bat species in the world. It is one of four species from the genus Pteropus that occur on the Australian mainland, but is the only one that is endemic to Australia. The majority of the flying fox diet comes from the blossoms of Eucalyptus and Banksia trees. When a flying fox feeds, its fur becomes covered in pollen. These animals are known to fly distances of up to 40km a night to forage, visiting a number of trees along the way. This makes flying foxes the most effective distributors of pollen, thus ensuring that Eucalypt forests maintain genetic diversity. This is of particular importance in fragmented patches of remnant urban bushland such as the Cooks River catchment, including the Wolli Creek Valley.

Flying foxes are often referred to as Fruit Bats and fruit is also an important component of their diet. Australian native fig trees, such as the Morton Bay Fig, are the most common fruit consumed by flying foxes. Australian rainforest trees depend on flying foxes to distribute their fruit seeds far from the parent tree in the same way pollen is carried long distances. Continued genetic diversity of rainforest and eucalypt forest is heavily reliant on healthy flying fox populations and vice versa.

Unfortunately, many people have not understood the importance of flying foxes and these animals have been neglected. Scientific estimates have shown that the population of the Grey-headed Flying fox declined by up to 30% between 1989 and 2001. In 2001, the Grey-headed Flying fox was listed as vulnerable in NSW, to protect the species from further decline. The rapid decline in Grey-headed Flying fox populations is associated with the clearance of vast amounts of native forest in Australia for agriculture, forestry and urban expansion, as well as a long history of conflict between people and flying foxes, mainly from misunderstanding.

Clearance and alteration of natural habitat has forced the flying foxes to find alternate habitat. As the diet of the Grey-headed Flying fox consists primarily of nectar, pollen, flower parts and fruit, the flying foxes need to migrate to areas where food species are in flower or fruit. The creation of urban environments has had a profound impact on the native wildlife and this includes the Grey-headed Flying fox. The modified environment of urban areas limits the available choices of roosting sites for flying foxes. Urban areas also create a considerable change in plant assemblages and although large areas of endemic flying fox food species are removed, there is an increase in introduced plant species of which flying foxes can take advantage. In urban areas it is often the case that modified plant assemblages provide reliable food sources for flying foxes at times when natural food sources are not available. The Grey-headed Flying fox, along with two other species of Pteropus, regularly form permanent colonies close to or within urban areas, to take advantage of more reliable food and water sources.

People have fears that their fruit trees will be raided at night by flying foxes. Studies have shown that flying foxes will prefer eucalypt flowers over fruit and tend only turn to fruit when gum trees are not in flower. The same studies have shown that when flying foxes do go for backyard fruit trees, they choose over-ripe fruit that has been left un-harvested. To protect fruit crops, harvest fruit before it ripens or tie paper bags over ripening fruit. Netting is not advisable as thousands of flying foxes, possums and birds are killed each year in improperly erected netting. If you feel netting is required, use a knitted variety with <40mm mesh sizes. It is extremely important to ensure that the net is stretched taut, preferably over a frame. Netting must be fully enclosed over the tree all the way to the ground so as not to let wildlife get underneath the net. Check the net for caught animals every day. If any animal is caught, immediately call a wildlife rescue group such as Sydney Metropolitan Wildlife Services (02 9413 4300) or WIRES (1300 094 737). Do not try to remove the animal yourself.

If flying foxes do visit your yard at night, you are lucky to have the company of such a wonderful native animal. If you hear flying foxes in your trees or see them flying overhead at night, wish them well and safe journeys. If you wish to get to know flying foxes better, the Botanic Gardens has a resident colony. For one of the most spectacular sights in nature, watch thousands of flying foxes fly out of the gardens at sunset. The best time to do this is in summer, from the bridge over the Cahill Express Way, near the Domain and Art Gallery.

If you wish to know more about flying foxes or bats in general, contact NSW National Parks and Wildlife Service or visit the Sydney Bats website.

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