The raccoon dog is a medium sized canid native to East-Asia. It was introduced to the western Soviet Union during the first half of the twentieth century, and has since then spread to, and established in, many European countries where it now is considered invasive. Raccoon dogs are suspected to have negative impacts on biodiversity, for example through nest predation, but empirical evidence is scarce. In this study we used GPS monitoring combined with camera traps on both artificial and natural nests to find out: (1) if raccoon dogs find and scavenge eggs from artificial nests, (2) if the scavenging from raccoon dogs is additive or compensatory to the scavenging from native species, and, (3) if raccoon dogs actively scare brooding birds off their nests and prey on their eggs. We found that raccoon dogs effectively located artificial nests and scavenged their eggs. There was a significantly higher scavenging frequency on experiment islands with both raccoon dogs and native scavengers, than on control islands with only native scavengers. There was no difference in native scavenging frequency on islands with versus without a raccoon dog, suggesting an additive effect from the raccoon dog on top of the native scavenging. GPStracked raccoon dogs moved intensively in the archipelago during the bird breeding season, swimming long distances to reach new islands if needed. Raccoon dogs that arrived on islands with natural nests actively scared brooding hens, up to the size of graylag goose, off their nests and preyed on their eggs. Raccoon dogs preyed on all the eggs they found, but discarded the egg shells. Not consuming the egg shells consequently leads to few visible traces of eggs in their stomachs or faeces, which in turn may explain why egg predation by raccoon dogs has been largely overlooked in previous studies. We discuss the potential impact of raccoon dogs on biodiversity, in the light of our new findings, and conclude that the raccoon dog may have a much larger effect on the breeding success of ground nesting sea birds than what has so far been the predominating view in the scientific literature.

Tularaemia is a zoonotic disease, in Europe caused by Francisella tularensis subsp. holarctica. Many lagomorphs and a variety of small rodents are wildlife species prone to develop clinical disease, while predators and scavengers are relatively resistant and may serve as sentinels. Blood samples from 656 Swedish wild predators and scavengers were serologically investigated using slide agglutination and microagglutination. In the slide agglutination test, 34 seropositive animals were detected, and they were found among all species investigated: brown bear (Ursus arctos), Eurasian lynx (Lynx lynx), raccoon dog (Nyctereutes procyonoides), red fox (Vulpes vulpes), wild boar (Sus scrofa), wolf (Canis lupus) and wolverine (Gulo gulo). Due to haemolysis the microagglutination test was more difficult to read at low titres, and only 12 animals were classified as seropositive. F. tularensis subsp. holarctica was detected by a polymerase chain reaction in lymphatic tissues of the head in one brown bear, one red fox and one wolf. The significance of this finding regarding possible latency of infection is not clear. In conclusion, the results of this study indicate that all predator and scavenger species included in this study may serve as sentinels for tularaemia in Sweden. Their role as reservoirs is unclear.

SummaryEfficient targeting of actions to reduce the spread of invasive alien species relies on understanding the spatial, temporal, and individual variation of movement, in particular related to dispersal. Such patterns may differ between individuals at the invasion front compared to individuals in established and dense populations due to differences in environmental and ecological conditions such as abundance of conspecifics or sex‐specific dispersal affecting the encounter rate of potential mates. We assessed seasonal and diurnal variation in movement pattern (step length and turning angle) of adult male and female raccoon dog at their invasion front in northern Sweden using data from Global Positioning System (GPS)‐marked adult individuals and assessed whether male and female raccoon dog differed in their movement behavior. There were few consistent sex differences in movement. The rate of dispersal was rather similar over the months, suggesting that both male and female raccoon dog disperse during most of the year, but with higher speed during spring and summer. There were diurnal movement patterns in both sexes with more directional and faster movement during the dark hours. However, the short summer nights may limit such movement patterns, and long‐distance displacement was best explained by fine‐scale movement patterns from 18:00 to 05:00, rather than by movement patterns only from twilight and night. Simulation of dispersing raccoon dogs suggested a higher frequency of male–female encounters that were further away from the source population for the empirical data compared to a scenario with sex differences in movement pattern. The lack of sex differences in movement pattern at the invasion front results in an increased likelihood for reproductive events far from the source population. Animals outside the source population should be considered potential reproducing individuals, and a high effort to capture such individuals is needed throughout the year to prevent further spread.