Heating up: Why Do Flying Foxes Suffer Through Heatwaves?

A friend of mine posted on my Facebook page asking about the mass flying fox deaths we have seen across the east coast of Australia (and in South Australia) in the past month or so. This is not an uncommon occurrence, particularly in south east Queensland, where the weather is known to maintain high temperatures for long periods of time. I had a bit of prior knowledge on this subject, as a previous Brisbane resident for around seven years, but when I was asked ‘what happened? why? and what can we do about it?’ I wanted to delve a little deeper into peer reviewed articles that address issues of mass death in flying foxes due to heatwaves.

What Happened?

During the last couple of weeks, heatwaves have hit the east coast, toasting the cities of Brisbane, Sydney and Canberra. Luckily in Melbourne, we missed the majority of the heat, but as typical South Australian weather dictates, Adelaide also succumbed to these ultra-sweaty weather events. The Bureau of Meteorology recorded extreme temperatures across the east coast (NSW, south east Queensland, ACT) frequenting the high 30s and reaching the early to mid 40s for days at a time. In this time, tens of thousands of bats were recorded as ‘dropping out of the trees’, with mass flying fox deaths recorded across the country.

It is not just a single species being affected; there are a number of species identified as being particularly at risk from these types of events. The ones we usually hear about are the grey-headed flying fox (Pteropus poliocephalus) and the spectacled flying fox (Pteropus conspicillatus) which are both listed as vulnerable under the EPBC Act(1999). The two more common species are the black flying fox (Pteropus alecto) and the little red flying fox (Pteropus scapulatus), both of which are listed as least concern. These ‘megabat’ species suffer equally from extreme heatwave events – But  why are we seeing such intense heatwaves?

flying-fox1

Grey-headed flying fox (Photo: Australian Mammal Learning Zone)

Why?

Locally, we can recognise effects such as the urban heat island effect (Manley 1958). This is a well recognised phenomenon where densely urbanised landscapes significantly affect the local climate, with the most recognised of these effects being increased temperature on hot days. Cities can reach up to 12 degrees higher than surrounding rural landscape (Oke 1979; Landsberg 1981), which can seriously affect the geographic distribution of plants and animals, as well as the behaviour of certain animals (Parris and Hazell 2005). Melbourne city has been estimated has averaging approximately 8 degrees higher than the surrounding area (VBC 2017), just as a local example. The loss of vegetation cover and the increase in heat-retentive concrete and bitumen combines to create a potentially devastating increase in temperature, particularly for animals with specific requirements or low tolerances. The lack of flying fox-preferred trees is another concern that is seriously affecting the persistence of these animals within our cities. An increase in human facilities will almost always come at a cost to remnant vegetation, particularly native forest, which has all but disappeared within intensely urban areas. This lack of resources and habitat has had a significant effect on bats worldwide, including here in Australia.

A Conversation article by  Welbergen, Booth and Martin (2014) discusses a particular behavioural trait which may explain why flying foxes tend to suffer greatly during heatwave events. The tendency for flying foxes to stay in roosts, and in groups, is a survival behaviour which would normally be advantageous to an individual’s survival. Unfortunately, when the flying foxes display this behaviour during a heatwave, it results in whole colonies dying, rather than finding shelter out of the sun. Of course, flying foxes are not the only animal that suffers mass casualties during these unprecedented heatwave events; examples of other animals are also linked in the Conversation article, so go and have a look if you are interested.

The overarching explanation of why these mass deaths occur is the elephant in the room; climate change. As most people are now aware, but I will reiterate here anyway, climate change encompasses far more than the typical ‘global warming’ we tend to associate with when hearing the term (hence why the name ‘global warming’ is no longer recognised as accurate). Climate change typically sees the significant increase in extreme weather events, including blizzards, heatwaves, floods and fires, among other weather phenomena. The increase in intense heatwave events is just one consequence we are seeing in Australia. The general consensus is that maximum temperatures and the frequency, intensity and duration of extreme heatwaves are set to increase (Welbergen et al. 2008, IPCC 2007). We are far more likely to see mass heatwave-related deaths of many species, particularly avian species (McKechnie and Wolf 2009). Unfortunately for them, flying foxes are one of the many ‘canaries in the coal mine’. The positive side of which is that the sensitivity of flying foxes to heatwave events can provide scientists with information on climate and weather events, by serving as bioindicator species. This also provides an opportunity for scientists to investigate how we may prevent these mass heatwave deaths into the future.

What can we do about it?

Even with events this seemingly widespread and catastrophic, there is always something everyone can do to support wildlife during heatwaves. As for flying foxes, there are some small things, and some not-so-small things we can all do to prevent the loss of these exceptionally important animals.

Flying foxes are critically important to a variety of ecosystems, particularly because they are highly mobile pollinators. Many fruits, in particular, are bat-pollinated and would not exist without the natural skill of flying foxes. It is in our own best interest to support flying fox colonies by establishing native gardens, particularly large native trees (if your property allows it). The increase in vegetation within our cities will be critical in combating the heat island effect, whether it be grass, shrubs or eucalyptus – any vegetation is better than none at all. More so than this, large native trees provide habitat and resources for flying foxes (amongst many other native animals). So if you are considering planting a garden, or renovating your existing one – think native! Some people may not want to encourage a colony of native bats onto their property, so alternatives to this may include assisting community groups to revegetate public areas, or writing to your local Minister and encourage them to increase the amount of native greenspace in your local area. Re-establishing flying fox habitat will help to support these fantastic animals, as well as kickstart cooling in your city.

There are a number of other contributions you can make to assist flying foxes, such as supporting positive State and Federal legislation which protects flying foxes, while if you find yourself in the company of one too many flying foxes at your orchard, garden or property, there are appropriate ways of dealing with flying fox colonies peacefully and respectfully. During heatwave days, it is difficult to provide much immediate assistance for flying fox colonies, but you can always try heading outside and watering them down! Seriously though, make sure you leave plenty of water out on hot days, not just for flying foxes, but for other wildlife.

The ultimate gift you may give your resident flying foxes is to become a carer with a wildlife organisation. All States will have a wildlife carer training program, which will equip you with the skills to care for animals that have been injured or displaced. Many States have very limited carers, and the less cuddly species such as flying foxes and reptiles are often the least staffed. Organisations such as WIRES (NSW), Wildlife ACT and wildlife Victoria will have regular training sessions where you can become a carer if you have the spare time. Of course, being a bat carer also requires a significant number of vaccinations, so keep this in mind if you are going to volunteer -but you only have to take a look at the Bats QLD Facebook page to see how rewarding this role is. Alternatively, there are a number of Bat Caring organisations you can donate to – I am sure you can google some in your area.

I hope this has provided you all with a little background information into one of the saddest events we see during extreme heat days, and has given you all a little confidence to give some of your time, effort, money or outdoor space to helping prevent heatwave deaths in the future. If we all contribute a little, there is nothing we can’t achieve.

Dr Mel.

Featured image: Buzzfeed Australia

References:

Environmental Protection and Biodiversity Act (EPBC) (1999). http://www.environment.gov.au/epbc.

Intergovernmental Panel on Climate Change (IPCC) (2007). http://www.ipcc.ch.

Landsberg, H. (Ed.), 1981. The Urban Climate. International Geophysics Series, vol. 28. Academic Press, New York.

Manley, G., 1958. On the frequency of snowfall in metropolitan
England. Quarterly Journal of the Royal Meteorological Society
84, 70–72.

Oke, T.R., 1979. Review of urban climatology, 1973–1976. World Meteorological Organization Technical Note No. 169. Secretariat of the World Meteorological Organization, Geneva.

McKechnie, A.E. and Wolf, B.O. (2009). Climate change increases the likelihood of catastrophic avian mortality events during extreme heat waves. Biology letters. Available at: http://rsbl.royalsocietypublishing.org/content/6/2/253.short.

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 polopcephalus) in Melbourne, Australia. Biological Conservation, 267-276.

Victorian Biodiversity Conference (VBC) (2017).

Welbergen, J.A., Klose, S.M., Markus, N. and Eby, P. (2008) Climate change and the effects of temperature extremes on Australian Flying-foxes. Proceedings of the Royal Society, B, 419-425.

Welbergen, J., Booth, C. and Martin, J. (2014). Killer Climate: Tens of thousands of flying foxes dead in a day. Available at: http://theconversation.com/killer-climate-tens-of-thousands-of-flying-foxes-dead-in-a-day-23227