Bringing the effects of artificial illumination on mammal diel activity patterns to light
Sam C Williams
Artificial light at night (ALAN) is an increasing source of anthropogenic pollution associated with changes in animal foraging behavior, migration patterns, and vigilance. We previously found mammals in sites with high ALAN have different diel activity patterns than those in sites with low ALAN. But, because ALAN is associated with urban environments, we could not separate the effects of ALAN from the effects of other human infrastructure. To determine the effects of ALAN on mammal diel activity, we directly manipulated ALAN levels at camera-trap stations illuminated by white, red, or no light. We hypothesized that all mammals would shift towards a more diurnal activity pattern to avoid ALAN, and that white light would have a greater effect than red light. We compared the number of diurnal and nocturnal observations of all mammals between stations with white lights, red lights, and no lights. We then conducted the same analysis three more times for observations of deer, gray squirrels, and raccoons. As hypothesized, a higher proportion of mammal observations occurred during the day at stations with ALAN present, and white light had a greater effect than red light. Deer exhibited a diurnal activity pattern at all stations, but the proportion of daytime observations was higher at stations with any ALAN present. As with all mammals, white light had a greater effect than red light on deer. In contrast to our hypotheses, ALAN had no effect at all on squirrels or raccoons. Overall, ALAN, apart from other types of human infrastructure, does affect mammal diel activity, but the effects are species-specific. The effects of ALAN can be partially mitigated by using red lights rather than white lights.
Sam Williams is a senior environmental science major from Greenville with minors in biology and chemistry. He previously won the Best Animal Biology Poster award at the Association of Southeastern Biologists meeting in Winston-Salem in 2023 and is continuing that research into this year with a new question.