Pureora Forest trial to shed light on bat behaviour

A trial is underway on the edge of the central North Island's Pureora Forest that will challenge the popular saying "as blind as a bat".

The collaboration between the Department of Conservation and Waikato University is monitoring the behaviour of native bats when different artificial coloured lights are in use.

DOC science advisor Kerry Borkin said although bats used echolocation as their primary navigation tool they actually had good vision.

"People often say, you know, blind as a bat but actually they've got pretty good eyesight and they're probably more sensitive to light we suspect from research overseas than people are.

"As you can imagine if you're geared up to be nocturnal then any light is possibly going to be blinding, but we're doing this research to see whether that is the case or not."

Borkin, who has 20 years experience working with bats, said they would not be harmed during the two-month trial, which is taking place on private property adjacent to the Pureora Forest - a known habitat for New Zealand's only native mammals.

"We've added some lights colours which we are turning on and off at regular intervals. But when we talk about light colour we don't mean the different coloured lights you put up on the Christmas tree.

"They are different colour temperatures that range from cool white light to a warm white light much like you can buy at the supermarket.

"Warm colour lights have less UV and blue wavelength than cool white or blue lights and can have a slightly yellow or amber tone. Bats are likely to be more sensitive to UV and blue wavelength light than humans because of the high proportion of UV sensitive rods present in their eyes."

Borkin said the colour could have a range of effects on bats and adding lights to an area could result in increases or decreases in bat activity depending on the species.

"So we've got monitoring equipment out that detects bats' echolocation calls and we are using that to count the echolocation calls each night and see if there's a difference between nights which have no lights and nights that have got lights in operation."

Determining how the bats responded to different colours of artificial light would help develop guidelines for councils installing lights in areas where bats were known to live, Borkin said.

"In the past we've always based our advice on overseas research about the effect of lighting on bats and this is our opportunity to find out whether lights have a similar impact on New Zealand bats and to base our guidance for people who are doing developments or have lights they are going to be placing in a certain area about how to manage those to minimise the impact on bats."

Waikato University PhD candidate Titia Schamhart said her particular interest was in how the artificial light impacted on the behaviour of long-tailed bats from both urban and rural environments.

"Specifically, I want to know whether different light spectra produce different behavioural responses, such as avoidance due to increased predation risk or attraction due to increased insect abundance around the lights."

Schamhart said the Pureora study would provide her with valuable experience in conducting this type of experimental trial, and form the basis of her own research planned in Waikato and Taranaki in the next couple of years.

"Ultimately, I hope my research will provide some insights into the potential impacts of artificial lighting on long-tailed bats and how these impacts might be mitigated by improved urban design."

The research phase of the project will conclude in March, before a period of data analysis.

JA Russell Ltd and Alf Downs Street Lighting have contributed lighting and electrical technology for this research work and the researchers said they were grateful for the active cooperation of landowners and iwi in the project.