Citizen science reveals the first occurrence of the greater white-toothed shrew Crocidura russula in Fennoscandia

Abstract The occurrence of the non-native, greater white-toothed shrew Crocidura russula in the Stavanger area in Southwestern Norway was brought to our attention by two records from the public (from 2012 and 2017). A citizen-science project, based on targeted media-calls between 2017 and 2019, resulted in 78 reported observations. A correct species identity, using photographs and collected specimen, was confirmed for 103 observations from 68 unique localities. Many of the sightings resulted directly from the media calls, but several were made both years before and after (ranging from 2012 to 2021). The minimum area of occurrence was 60 km long and 20 km wide and is characterised by one of the mildest climates in Norway. No clear expansion pattern was evident from the data, though an introduction between 2000 and 2010 seems likely. As only a few other shrew species were reported by the public, it is possible that the white-toothed shrew has outcompeted native shrews in the area. However, this could be biased by the nature of the media call or the commensal lifestyle of the shrew. Media calls beyond the area of occurrence did not result in any reports of the species. The introduction route and origin of the present population remain unclear.