Why do flying-foxes like to live in cities?

A grey-headed flying-fox; photo by Ian Kitchen

Flying-foxes are big bats – the biggest in the world!  They belong to a group of mammals known as the Megachiroptera (pronounced “megga-kai-roptera”) or megabats.  Unlike their smaller cousins (the Microchiroptera or microbats), they like to eat fruit, pollen and nectar rather than insects.  Megabats are only found in the southern hemisphere, and they mostly live in tropical and subtropical parts of Africa, Asia and Oceania.  So flying-foxes like their food vegetarian and their weather warm and humid.

During the day, flying-foxes hang around together in big groups called camps – and I mean hang!  They sleep hanging upside down in trees, but they also spend quite a bit of time chattering to each other and jostling their neighbours to get a better position when things are a bit crowded.  Flying-foxes are very social animals!  At night time, they fly out from the camp to look for food.  This is known as foraging, and some flying-foxes can travel up to 50 km in one night to find a good dinner and then get home again.

The biggest camps of Australia’s grey-headed flying-fox can hold 200,000 animals at a time.  In the past, this species mainly camped in natural areas like sub-tropical rainforest, Eucalyptus forest and Melaleuca swamps.  But recently, more grey-headed flying-foxes have been camping in cities, bringing them into closer contact with people.  Old camps in Sydney and Melbourne have been getting larger, and new camps have appeared in cities such as Geelong, Bendigo and Adelaide.

Grey-headed flying-foxes at Yarra Bend, Melbourne; photo by Kirsten Parris

In 2003, a camp at the Royal Botanic Gardens Melbourne was moved to a new site on the Yarra River.  More flying-foxes had been arriving at the camp every year, and people were concerned that they were damaging some important trees in the Gardens.  The Royal Botanic Gardens Sydney is currently trying to move their flying-fox camp, for similar reasons (see ABC Radio National for an interesting story about the Sydney relocation).

So why do flying-foxes like to live in cities?  Wouldn’t it be nicer for them in the forest?  Well, there are a few reasons:

1.  There’s not much forest left.  Huge areas of sub-tropical rainforest, Eucalyptus forest and coastal Melaleuca swamps have been cleared since the European settlement of Australia.  One example is the Big Scrub, an area of sub-tropical rainforest in northern New South Wales that used to cover 75,000 hectares of land.  More than 99% of this forest was cleared for farming during the 1800s, and now only about 100 hectares remains (perhaps it could be renamed the Very Small Scrub).  These days, most clearing of forest and swamps along the east coast of Australia is for urban development such as new houses, roads and shopping centres.

2.  City parks and gardens provide pleasant camp sites, and the city and suburbs can supply tasty food for flying-foxes, all year round.  For example, there are more than 300,000 street trees in Melbourne that provide fruit and nectar for grey-headed flying-foxes to eat.  Many of these trees belong to species that do not naturally occur in Melbourne.

3.  In southern Australia, cities are getting warmer.  Due to something known as the urban heat-island effect, cities are often warmer than the surrounding countryside.  And as cities grow, the effect gets larger.  Temperatures in central Melbourne have been increasing since the 1950s, leading to warmer conditions (particularly at night) and fewer frosty mornings.  Also, watering of city parks and gardens – to keep them green and lush during the warmer months of the year – acts like extra rainfall.  So parts of Melbourne are now warm enough and wet enough for grey-headed flying-foxes to stay all year round.

You’ve probably noticed that all these reasons have something to do with people.  People have changed the environment for flying-foxes in Australia by clearing large areas of their natural habitat and making new habitats for them in cities.  Is it surprising that they have decided to move in with us?

Grey-headed flying fox; photo by Ian Kitchen

More information about flying foxes:

The Australasian Bat Society

DSE Victoria – Facts about bats and flying-foxes

Hall, L.S. and Richards, G. (2000). Flying Foxes: Fruit and Blossom Bats of Australia. University of New South Wales Press, Sydney.

Parris, K.M. and Hazell, D.L. (2005). Biotic effects of climate change in urban environments: the case of the grey-headed flying-fox (Pteropus poliocephalus) in Melbourne, Australia. Biological Conservation 124, 267-276.

van der Ree, R., McDonnell, M.J., Temby, I.D., Nelson, J. and Whittingham, E. (2006). The establishment and dynamics of a recently established camp of flying-foxes (Pteropus poliocephalus) outside their geographic range. Journal of Zoology 268, 177-185.

Williams, N.S.G. et al. (2006). Range expansion due to urbanization: Increased food resources attract Grey-headed Flying-foxes (Pteropus poliocephalus) to Melbourne. Austral Ecology 31, 190-198.

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