The impact of the lunar cycle and season on small mammal communities near a large metropolitan area

Abstract

Small mammals are prey to a range of predators and consequently use environmental cues, such as light, to assess the level of predation risk in their environment. The lunar cycle significantly influences the fear landscape for prey species because their risk level varies with visibility. We conducted small mammal surveys in two communities in close proximity to each other on a peri-urban site in South Africa. We investigated the abundance, composition and diversity of these communities across the lunar cycle and seasons. As predicted, we trapped the highest number of individuals and species on new moon nights, which have low light levels and thus indicate a reduced perceived predation risk. Winter showed a higher abundance compared to the other seasons, which could be explained by a decline in naturally available resources in winter. We captured more individuals and species on one site compared to the other site, largely because of the different microhabitats in the two sites; one site had a lower density of trees and more bare soil areas. Our study provides the first evidence of the impact the lunar cycle has on small mammal communities in southern Africa. Based on our findings of decreased activity of small mammals under increased lunar visibility, we hypothesise that small mammal communities in southern Africa will be negatively affected by the increased occurrence of artificial light at night, which could have wider ecosystem impacts.