Diet of the raccoon dog, an invasive mesopredator, during the breeding season of declining waterbird populations

Abstract

Invasive predators are one of the leading causes of global biodiversity loss, threatening local ecosystems through predation and spreading diseases. In Europe, the most common and widespread invasive mesopredator is the raccoon dog (Nyctereutes procyonoides). Raccoon dog is an opportunistic omnivore listed as a species of European Union concern, as they are suspected of harming ground-nesting waterbird populations. However, the actual extent of risks caused by raccoon dog predation has been disputed, partly due to methodological constraints in detecting all prey in the diet. Here, we studied the animal components of raccoon dog diet using DNA metabarcoding, a powerful tool to detect even the smallest traces of ingested food items. We sequenced genes 12S rRNA and COI from raccoon dog scat samples collected during the breeding season of birds close to water bodies in southern Finland. We also examined whether the occurrence of different dietary items would depend on the habitat around the latrine. We found that frogs were the most common vertebrate food item in raccoon dog diet during spring. The proportion of detected bird material was not higher compared to earlier studies, despite the potential to detect DNA originating from eggs. The proportion of fish in the diet increased with increasing water area around the latrine, but no other relationships between diet and habitat were found. We conclude that even though raccoon dogs predate on waterbirds’ and other ground nesting birds’ nests, they do not seem to be specialized on it in our study areas. However, declining waterbird populations and, in particular, local amphibian populations could be negatively impacted by raccoon dog predation.