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Bats and Lighting

Two of the major findings of SCF’s 2017 Common user survey, were concerns about safety on The Common and a strong desire for better natural and artificial lighting on the main paths, most of which are currently unlit, though historically more were lit. This has also been an issue for plans for improving Lovers’ Walk where Council proposals have repeatedly failed to include lighting the unlit lengths, contrary to police advice.

Whilst police statistics actually show The Common to be a very low risk area, the perception of danger is very real and undoubtedly contributes to many avoiding it in the dark. A main argument against lighting the paths has been claims that it would disturb wildlife, especially the many species of bat which are found occur in and around The Common. However, it is believed that most of the bats using The Common actually roost away from it and travel in, across well lit urban areas with plentiful street lighting, including The Avenue, so clearly the bats don’t avoid street lights as such, and some actively exploit them by feeding on the insects that are attracted to conventional street lighting. In short, there was no actual scientific evidence for adverse effects of lighting on The Common’s bats, but clear data to support the need for lighting for human users.

In an attempt to reconcile the opposing views and provide an evidence base to inform future management decisions, SCF convened a bat expert advisory group comprising SCF, bat ecologists from The University of Southampton, Hampshire Bat Group and the Bat Conservation Trust, Council Parks and Ecology teams and Southampton Common and Parks Protection Society (SCAPPS).

As a result of this group, contact was made with Signify, the lighting division of the Philips electronics group. Signify have developed a red led based street light luminaire (ClearField) which had been shown in extensive trials in rural Netherlands to be “bat neutral”. ClearField had not been tested in the UK and had never in an urban context. This presented the perfect opportunity for a collaborative experiment on on The Common and Signify kindly loaned us 2 standard while LED luminaires and 2 ClearField luminaires to test.

Over the course of summer 2019, Rosie Hopkins, a masters student at Southampton doing the work as her dissertation, and a team of SCF volunteers conducted lighting trials at 8 sites on unlit paths across The Common, 3 nights at each site (ideally consecutive but weather dependent - cold, rain or wind all affect bat activity). Two 3.3m high lighting columns were erected 30m apart with a recording bat detector positioned mid way between them.  1 night  used white lighting, one used ClearField lighting, the other was unlit but with lighting columns in place and generator running under load to control for sound and physical disturbance. The order of conditions was varied between sites).Data was collected continuously for a 3.5 hour period from sunset on each night, with environmental conditions recorded every 30 minutes. was In addition, on ClearField nights a questionnaire was used to assess user reaction to the red lights. Back in the lab, Rosie analysed the recordings for species and activity type.

Copyright © Southampton Common Forum - 2021

Copyright © Southampton Common Forum - 2021

 A total of 13,198 bat passes were analysed from over the 24 experimental nights, including 1,159 feeding buzzes and 974 social calls

Bat call analysis showed:

Public perception (91 questionnaires over 11 nights) was largely positive

These experiments indicate that paths on The Common could be lit without adversely affecting wildlife, especially if the lights are installed in concert with other measures, including the use of motion sensors, deactivation during hours of minimal use etc.. Together this would form an effective mitigation strategy to prevent adverse impacts on wildlife at the same time as increasing night-time public comfort and safety on Southampton Common for recreation, exercise and green travel.

summary report  -  full dissertation

Bat calls recorded at the Ornamental Lake during the study

Word cloud of responses to “how safe would you feel with red lights?”

Word cloud of responses to “would your opinion change knowing the red lights were less disruptive to wildlife?”

SCF thanks the Bat Expert Advisory Group for its help, Signify for loan of the luminaires, Jack Merriman for loan of lighting columns, Orly Razgour for project supervision and loan of bat recorder and especially Rosie (Rozel) Hopkins for running the experiments (for which she was awarded a well deserved Msc with distinction) and all of the SCF volunteers who stayed up very late into the sometimes chilly summer nights to help with the experiments.