Artificial nest predation, relative abundance, and activity patterns of mesocarnivores in relation to wild boar presence

Intensifying nest predation is one of the suggested factors causing the wide decline of ground-nesting birds. Predation rates often increase with growing predator numbers, especially of invasive species. The emerging effects of novel species may, however, be hard to quantify due to interactions with native species. The wild boar (Sus scrofa) has recently expanded its range into Finland through natural dispersion, marking a significant northward extension of the range. In this ecosystem, little is known about the direct and indirect roles of wild boars as nest predators. Especially the potential avoidance of wild boars by other mammalian nest predators has not been studied. To address this gap, we conducted artificial nest and scent post experiments with camera traps on sites of wild boar presence and absence. We found that predation rates by wild boars were at similar modest levels than the rates of other mammalian predators in the area. No significant differences in the overall likelihood of nest predation or nest visits by mesocarnivores were observed between the study areas. Based on the scent post indices, however, mesocarnivores were less abundant on wild boar sites. Our study concludes that the effects of wild boars on nest survival rates are small at their current low densities. The study also provides a baseline for monitoring, as wild boars are expected to expand their range and density in the future.