Can artificial lighting be ‘wildlife-friendly’? Testing the impact of PC amber LED light on bat emergence behaviour

Artificial light at night can negatively impact nocturnal species such as bats through loss of landscape connectivity, foraging and roosting opportunities. Lighting manufacturers are developing and marketing long wavelength (amber and red) LED lighting as ‘wildlife-friendly’, however, the impact of this new technology on wildlife is not fully understood. Here, we use an experimental approach to compare the effects of two different LED colour spectra on the emergence behaviour of a threatened UK bat species, Rhinolophus hipposideros . Bats were exposed to two different lighting treatments, ‘PC amber’ (1750 K) and white (4000 K), while emerging from their maternity roosts in South West England. Both lighting types negatively affected bat emergence behaviour (increased inter-emergence interval and delayed colony median emergence time) compared to the control. The response to white LED light was stronger than PC amber, and also led to a reduced total emergence count. We find that PC amber lighting negatively impacts emerging bats, challenging the idea that long wavelength light is ‘wildlife-friendly’ and highlighting the importance of considering behavioural context, species- and spectral-specific responses when assessing the impact of artificial light at night on biodiversity. We recommend that strong, robust evidence for the impact of long wavelength LED light is needed to inform lighting mitigation strategies before this new technology is widely adopted.