Like a bat out of hell, Long-tailed bats are gone when the lights turn on

The presence of artificial lighting affects New Zealand’s beloved but endangered Long-tailed bat, and researchers are now able to show how.

When the lights are on, the bats arrive later, and in smaller numbers.

These are the findings of a small-scale study conducted by University of Waikato researcher Titia Schamhart and co-authors conducted on the outskirts of Hamilton city in the North Island.

The paper published in the New Zealand Journal of Zoology contributes to understanding of the effects of artificial lighting on the Long-tailed bat. 

“Long-tailed bats are endangered, declining rapidly and can’t be bred in captivity. With the ever increasing urbanisation, light pollution is a potential big threat for them, one which is easily remedied so let’s start there,” Schamhart says.  

The Long-tailed bat (Chalinolobus tuberculatus) is one of only two bat species native to New Zealand, which are also the country’s only native terrestrial mammals. So beloved is the species that it famously won a popular vote for New Zealand Bird of the Year in 2021.

Schamhart’s study measured Long-tailed bat activity at a home with a large garden with around 70 mature kahikatea trees. 

A previous owner had installed lighting at some of these trees, providing the researchers with an opportunity to compare bat activity on nights when the lights were on, and off, as well as at a control site with no lighting located approximately 150m away within the same property. 

Bat activity at the site was monitored using ultrasonic recorders between October and December 2020, a period when long-tailed bat activity is more likely to be high. 

When the lights were turned on, the first bats recorded arrived around 2 hours later (median) than the control sites, Schamhart says.

“The bats were always way later to the party when the lights were turned on. And there was also a big, big difference in the number of bats … with the lights on, compared to the control site and with the lights off,” she says.

Schamhart says bats in general are thought to avoid lighting as this makes them vulnerable to predators. But other researchers have suggested that fast flying bats may be less affected given their ability to take advantage of the insects attracted to lights while also escaping predators.

For example, a Brisbane-based study by University of Queensland researcher Rani Davis, showed the fast-flying White-striped free-tailed bat was less deterred by artificial lighting than the slightly slower Little bent-wing bat.

Yet despite the Long-tailed bat being capable of reaching speeds of around 60km/hr, the results from the Hamilton study show fewer bat recordings and delayed arrival in the presence of lighting.

The findings of the study are significant given the species is listed as nationally critical by New Zealand’s Department of Conservation, and with urban expansion (accompanied by lighting) is encroaching on the bat’s habitat.

By understanding how the bats behave in response to night lighting, these impacts may be mitigated, Schamhart says. 

As well as establishing a charity for bat research, Schamhart is further investigating the effects of lighting on bats in other parts of the country and whether filtering light colour might make a positive difference.