Artificial nest experiments demonstrated that the raccoon dog, an alien species abundant in Finland, is a more common duck nest predator than any indigenous mammalian species. The species depredated nests on shorelines as well as in forests, rural landscapes and urban areas.

A new study proves the suspicions well-founded. In experiments carried out over three years by the University of Helsinki, Finland, and Aarhus University, Denmark, wildlife cameras recorded an abundance of images of alien species predating artificial nests established by the researchers in Finland and Denmark.

More than 400 artificial nests containing farmed mallard eggs were created, of which roughly 290 were located around southern Finland. The nests were built in natural duck nesting environments. In Finland, raccoon dogs (Nyctereutes procyonoides) were more common nest predators than red foxes, although in Denmark the situation was reversed, possibly reflecting the species local relative abundance.

«The raccoon dog was the most common mammalian predator in all of the environments studied in Finland. As expected, raccoon dogs destroyed nests on shorelines, but surprisingly often also in forests close to wetlands,» says Postdoctoral Researcher Sari Holopainen from the Finnish Museum of Natural History Luomus, University of Helsinki.

Broken eggs attract mammalian predators

Wildlife cameras revealed that many nests were visited by more than one predator. Corvids were often the first to notice the nests. On occasion, they would break an egg in the nest, which would attract mammalian predators to the spot. American minks and raccoon dogs often visited nests previously predated by others.

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