Environmental DNA reveals a presence of <i>Anser fabalis</i> (Bean Goose) and an absence of <i>Anser erythropus</i> (Lesser White-fronted Goose) in Finnish Northern Lapland

ABSTRACT Detecting rare and elusive species from vast wilderness areas poses significant challenges. The Fennoscandian population of Anser erythropus (Lesser White-fronted Goose) is among the most endangered bird populations in Europe, with only 25–30 breeding pairs remaining in Northern Norway. Historically, its former breeding range extended across the mountainous regions of Fennoscandia. Thanks to targeted conservation efforts during the 21st century, A. erythropus has started to recolonize some of its former breeding areas in Norway and possibly also in Finland. Anser serrirostris rossicus (Tundra Bean Goose) is classified as Endangered in Finland, with just a few breeding pairs in northernmost Finnish Lapland with a poorly known breeding range. It breeds in higher numbers in Finnmark Norway and is listed as Vulnerable in Norway. Anser fabalis fabalis (Taiga Bean Goose), classified as Endangered in Norway, can also breed in the same area in low numbers. To locate individuals of these elusive goose species during breeding seasons, we used environmental DNA (eDNA) extracted from filtered lake water from selected lakes in northern Finland. We amplified and sequenced a short region of the mitochondrial control region to identify the species. Additionally, for positive controls, we sampled eDNA from the water of a Finnish spring staging site and known Norwegian breeding sites of the A. erythropus, from which eDNA of the A. erythropus was identified. eDNA of the A. erythropus was not detected within the former Finnish breeding range. Based on this, the A. erythropus has either not recolonized its former breeding habitats in Finland, the correct lakes were not sampled, the eDNA concentration was below detection limits, or due to other methodological issues. Anser s. rossicus was detected in 3 lakes and A. f. fabalis in 10 lakes, providing new information about the breeding distribution of Bean Geese in Finnish Lapland.