The effects of artificial nighttime lighting on moth visual ecology and survival

Artificial light at night, from streetlights and other sources, is increasing at unprecedented rates, in terms of intensity and worldwide coverage. This lighting almost certainly has wide-ranging effects on the visual ecology of nocturnal animals, and has been implicated in the dramatic population declines of nocturnal moths throughout Europe.

Many nocturnal moths use their outstanding low-light colour vision to locate flowers at night and are major global contributors to pollen transport networks. Recent research has highlighted the potential for artificial light sources to interfere with the vision of nocturnal pollinators, change their abundance and distribution across landscapes, affect pollination quality, and alter their response to predators. Attraction to light sources is also a well known cause of mortality in many insects. Nevertheless, much of this research remains correlative, or limited to specific species, and a fundamental behavioural understanding is lacking of how different artificial light sources affect specific visual interactions that are key to the survival of moths and the plants they pollinate.

Our visual modelling work identified unexpected interactions between light type, light intensity and object colour, for example allowing the same flower to change from highly conspicuous to a background-matching colour dependent on light intensity. Such effects could fundamentally disrupt pollinator behaviour in a manner that would be almost impossible to detect in the wild, and with unknown consequences for plants. Our modelling also suggested that artificial light could interfere with the anti-predator defences of moths by causing poor choices of background colour for daytime resting.

This project will determine how nighttime artificial light affects three key aspects of moth visual ecology: i) Floral signalling: we will investigate the predictions of our visual modelling using semi-natural experiments, testing the effects of complex interactions between light type, light intensity and flower colour on visually-guided flower detection and handling behaviour. ii) Flight behaviour: tethered flight experiments using simulated viewing conditions will be used to determine how different moth species respond to different aspects of artificial light and background scene appearance, and which hypothesised orientation mechanisms are affected. Specifically, this will measure the attraction, repulsion or flight deflection of different light sources at different intensities, distances and background contrasts. iii) Anti-predator defences: predation is the main source of mortality in many species, and our modelling suggests that artificial light sources could weaken this defence. A combination of moth background choice experiments and controlled predation experiments will determine how nighttime background choice under different types of artificial light affects predation risk from visually-guided avian predators in the daytime.

Fulfilling these three objectives will provide the first assessment of the potential impact of novel light sources on the visual ecology of moths (or any animal). Critically, by determining how and why specific types of artificial light interfere with key behaviours and interspecific interactions we will be able to assess their likely impact on pollination and moth survival, which will in turn affect the biodiversity of wildflowers and other pollinator groups, with implications for food security. Moreover, the results will facilitate the development of targeted mitigation strategies from whole-taxon levels, right down to species-specific interactions. This is critical because next-generation light sources identified as potentially disruptive to pollination behaviour in our modelling are already being deployed.