Alien species are recognised as presenting an increasingly global threat to native species, but we often lack evidence of their interactions and effects. For example, boreal nesting duck species have recently declined in abundance and in Finland more than half of the species are now classified as endangered. Alien predators have been suspected as playing a part in these declines and new studies suggest that this suspicion is justified. A joint Helsinki and Aarhus University study established more than 400 artificial nests containing farmed mallard (Anas platyrhynchos) eggs in normal duck nesting sites in Finland and Denmark, monitoring nest fates with wildlife cameras.
The invasive alien raccoon dog (Nyctereutes procyonoides) proved to be a more frequent and opportunistic predator than any of the native predator species. In Finland, raccoon dogs were more common nest predators than red foxes (Vulpes vulpes), although in Denmark the situation was reversed, possibly reflecting the species local relative abundance: the raccoon dog already ranks second/third among the most numerous species killed annual by Finnish hunters. The studies showed that raccoon dog was the most common mammalian predator of artificial nests in all duck nesting habitats, predating nests on lake shores as well as in forests, agricultural landscapes and in urban areas, whereas the presence of individual native mammal predators was restricted by habitat type. The other alien species, American mink (Neovison vison) was less frequent at artificial nests as the primary predator, but often visited nests already depredated by others. Corvids, which regularly broke eggs at artificial nests, were often the primary predators. Nests with broken eggs significantly attracted mammalian predators, hence inter-guild facilitation can contribute to an enhanced impact from diverse predatory communities equating to more than the sum of that of their constituent species. Both alien species not only take eggs, but also readily depredate sitting hens.
While it is clear that artificial nest experiments cannot directly demonstrate an effect of alien species on duck populations, the decline of nesting populations of many waterbird species in Finland coincides with increasing abundance of raccoon dogs and American minks and it seems unlikely that other ground-nesting birds are not suffering similar attentions from these predators . Controlling such predator species and preventing their dispersion, especially alien species like raccoon dog, is heavily resource demanding but has been achieved in Sweden. The success of such coordinated and concentrated control suggests that such conservation actions could have the potential to improve boreal duck breeding success, while bringing potentially far wider ecological benefits.
Read more:
Holopainen S, Väänänen V-M, Fox AD (2020) Artificial nest experiment reveals inter-guild facilitation in duck nest predation. Glob Ecol Conserv e01305.
Holopainen S, Väänänen V-M, Fox AD (2020) Landscape and habitat affect frequency of artificial duck nest predation by native species, but not by an alien predator. Basic Appl Ecol 48: 52–60.
Krüger , H , Väänänen , V-M , Holopainen , S & Nummi , P 2018 , ‘ The new faces of nest predation in agricultural landscapes : a wildlife camera survey with artificial nests ‘ , European Journal of Wildlife Research , vol. 64 , no. 6 , 76 . https://doi.org/10.1007/s10344-018-1233-7
Holopainen S, Väänänen V-M, Vehkaoja, M, Fox AD. Do alien predators pose a particular risk to duck nests in Northern Europe? Results from an artificial nest experiment. Online early, Biological Invasions.
Pöysä H, Linkola P (2021) Extending temporal baseline increases understanding of biodiversity change in European boreal waterbird communities. Biol Conserv 257: 109139.
Close Encounters of the Natural Kind 