Are artificial lights driving microbats.... batty?

This is a guest article by ecologist Grant Linley.

Their looks are the stuff of nightmares, they are continually urbanising and colonising new environments, and they have had disastrous impacts on the environment so far. These thoughts might go through the brain of Microchiropteran bats when thinking about humans. Whilst some may reel at their looks, their uniqueness makes them quintessentially Australian. These small, flying mammals are all around us at night and they live unheard and unseen among us. Insectivorous bats are a diverse and adaptable group of mammals that has been able to persist among environments that have undergone large scale changes due to urbanisation, making them a true Aussie battler.

Insectivorous bats are known to eat up to half their body weight in insects each night, with some eating up to 600 mosquitoes a night. Not only do they play an important role in keeping invertebrate species in balance, but in doing this they also promote plant growth and pollination. This makes them a key species in keeping urban ecology in balance. To help understand what affects insectivorous bats within urban environments, I conducted a study that considered the impacts of artificial lighting in Melbourne’s south-eastern suburbs. Using an Anabat Express (a gadget that helps us listen in on bat vocalisations), ultrasonic calls were recorded and used to identify species in artificially lit and unlit areas.

The Gould’s wattle bat (Chalinolobus gouldii) smiles for the camera. The study found that they were the most common species to occur along Bayside’s foreshore. Image: Lindy Lumsden

The Gould’s wattle bat (Chalinolobus gouldii) smiles for the camera. The study found that they were the most common species to occur along Bayside’s foreshore. Image: Lindy Lumsden

 

HOW DOES ARTIFICIAL LIGHTING AFFECT BATS?

Within the coastal vegetation in the Bayside area, I found unlit sites to have higher numbers of calls and species richness when compared to lit sites. Almost all of the identified species were adversely impacted by artificial lighting, specifically Austronomous australis, Chalinolobus morio, Miniopterus schreibersii oceanensis, Mormopterus spp, Myotis macropus, Nyctophilus geoffroyi, Saccolaimus flaviventris, Vespadelus darlingtoni and Vespadelus regulus. Lit sites attracted bats at lower temperatures than unlit sites and bat activity remained active throughout the night at unlit sites. However, at lit sites bat activity quickly diminished in the hours after sunset.

The effects of artificial lighting on insectivorous bats are complex and likely to be caused by a variety of reasons. All species that are susceptible to artificial lighting, except V. regulus, have larger bodies that are less manoeuvrable. It is thought that a lack of manoeuvrability may force these species away from lit areas, as they are not able to capture prey that is attracted to the lights. It is possible that artificial lighting causes changes in activity of bats at different temperatures because it interferes with insect navigation systems, making insects active at lower temperatures and in turn attracting bats during these times. The difference in bat activity throughout the night is thought to be caused by a rapid decrease in insect density around light sources as time passes after sunset, which forces bats to go in search of their prey in unlit areas.

 

WHAT CAN YOU DO FOR THEM?

Artificial lighting on the foreshore in the municipality of Bayside has impacted bats and appears to fragment parts of the landscape. The negative impacts on insectivorous bat activity will likely increase as more street and safety lights are installed in urban areas. In the future, safety lighting systems should be installed in car parks and walkways that are activated by a sensory switch and only remain on for a short period of time. Councils should also consider minimising the use of mercury vapour lighting, which attract larger insect loads than low-pressure sodium lamps. Additionally, members of the local community can build and install bat boxes, which provide bats somewhere to roost. Unfortunately, suitable habitat for these species is constantly diminishing within suburbia. These findings will be published shortly.

Banner image by Scott Sanders (via Wikimedia Commons).


Grant Linley

Grant is an ecologist interested in Australia's flora and fauna. He has experience researching, trapping, tracking, identifying and handling different Australian species. Whilst experienced in terrestrial Australian ecology, he has also conducted research in Borneo and South Africa. Grant's interests centre on preserving and reintroducing extant and extinct Australian species as well as using natural predators to control mesopredators.