Flight-to-light and the decline in British moths

Abstract

More than 80% of Europe is now under artificially brightened skies with light pollution continuing to grow annually in both extent and intensity. The nocturnal landscape is highly heterogeneous, varying in intensity and emission, with the continued transition to LEDs associated with an increase in potentially more ecologically damaging shorter light. Detrimental impacts of artificial light have been found for several key behavioural and physiological processes in moths, leading to the suggestion that light pollution has contributed to their population declines. The aims of this thesis were to identify the impacts of wavelength on flight-to-light behaviour of moths when separated from the confounding variables of bulb design and intensity, and to quantify the impacts of light pollution on moth populations at two temporal resolutions using data from the Rothamsted Insect Survey (RIS) light trap network. Short wavelengths attracted significantly more moths than long wavelengths and blue light was found to supress the onset of flight activity. Neither flight-to-light or suppression of flight were impacted by moderate changes in light intensity at a fixed wavelength. To enable light pollution to be measured at an ecologically more relevant scale, a new high-resolution light-pollution map of Great Britain (GB) was compiled using night-time satellite imagery from the Luojia1-01 satellite. This provided high quality coverage for 62% of terrestrial GB at a resolution of 130 m (compared to >700 m resolution of previously available night-time light monitoring products). Using classifications based on this map, moth abundance was found to have declined significantly at lit sites but not at dark sites in the 28-year period since 1990, providing correlative evidence for light pollution as a driver of observed moth population declines. Nightly sky brightness data collected at a subset of Rothamsted sites had no relationship to nightly moth trap catches in open habitats. However, site-specific analysis found lunar cycles in catch data at >85% of sites with no evidence of dampening of this cue in the presence of skyglow. Together these findings highlight the detrimental impact of direct artificial light exposure on moths at an individual and population scale, although the impacts of skyglow are still unclear.