Abstract
Several alien predator species have spread widely in Europe during the last five decades and pose a potential enhanced risk to native nesting ducks and their eggs. Because predation is an important factor limiting Northern Hemisphere duck nest survival, we ask the question, do alien species increase the nest loss risk to ground nesting ducks? We created 418 artificial duck nests in low densities around inland waters in Finland and Denmark during 2017–2019 and monitored them for seven days after construction using wildlife cameras to record whether alien species visit and prey on the nests more often than native species. We sampled various duck breeding habitats from eutrophic agricultural lakes and wetlands to oligotrophic lakes and urban environments. The results differed between habitats and the two countries, which likely reflect the local population densities of the predator species. The raccoon dog (Nyctereutes procyonoides), an alien species, was the most common mammalian nest visitor in all habitats and its occurrence reduced nest survival. Only in wetland habitats was the native red fox (Vulpes vulpes) an equally common nest visitor, where another alien species, the American mink (Neovison vison), also occurred among nest visitors. Although cautious about concluding too much from visitations to artificial nests, these results imply that duck breeding habitats in Northern Europe already support abundant and effective alien nest predators, whose relative frequency of visitation to artificial nests suggest that they potentially add to the nest predation risk to ducks over native predators.
Highlights
Predation pressure seems to be the most important factor affecting nesting success in boreal breeding ducks (Holopainen et al 2015)
Based on all nest visits by the five most common mammalian predators, raccoon dogs visited nests significantly more often than the other four other species (Table 1). This pattern differed between the countries: in Denmark, the native red fox, European badger and martens visited the nests more often than raccoon dogs
Our results showed that among the variety of contrasting northern European duck breeding habitats investigated in this study, the raccoon dog proved to be ubiquitous in a way not reflected among the native predator species, contrary to our hypotheses
Summary
Predation pressure seems to be the most important factor affecting nesting success in boreal breeding ducks (Holopainen et al 2015). Populations of egg-consuming predators are considered to have increased during the last five decades in Europe (Kauhala 1996; Panek and Bresinski 2002; Roos et al 2018), affecting nesting success of water birds (MacDonald and Bolton 2008; Brzezinski et al 2019). In addition to native species, several invasive alien predator species have become dispersed widely in Europe, such as the raccoon dog (Nyctereutes procyonoides), American mink (Neovison vison) and raccoon (Procyon lotor, Kauhala 1996). A review showed that the effect of American mink on ground nesting birds is significant (Bonesi and Palazon 2007), while for the raccoon dog (Mulder 2012) and raccoon (Salgado 2018) ( less well studied) the pattern was not so clear. The presence of just a few individual raccoon dogs can have major adverse impacts on inland nesting waterbird colonies (Koshev et al 2020)
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