Danish researchers ask public to report signs of endangered hazel dormouse

Researchers at the University of Southern Denmark are calling on the public to help locate the endangered hazel dormouse, a rare rodent believed to be in sharp decline across the country, DR reports.

Biologist Zenia Henriksdottir Hansen, leading a PhD study on the species, said current population estimates remain uncertain, but evidence suggests the hazel dormouse is disappearing from known habitats. While confirmed populations exist in southern Funen and parts of Zealand, a 2024 discovery in Draved Forest, South Jutland—where the species had not been recorded for over 13 years—has raised hopes of undiscovered groups elsewhere.

National monitoring under the NOVANA program surveys for the species only every six years, focusing primarily on previously documented areas. “It would be physically impossible for us to survey the entire country alone,” Hansen said, emphasizing the need for public involvement.

The hazel dormouse, though named like a mouse, is not a pest and avoids human contact, researchers stress. Its presence serves as an indicator of healthy ecosystems, benefiting a wide range of other species from insects to larger mammals.

Members of the public are urged to search for three key signs:

Hazelnuts with distinctive bite marks The hazel dormouse leaves smooth-edged holes in hazelnuts, often surrounded by small, precise tooth marks—unlike the rougher gnawing of other rodents or the clean breaks made by squirrels. Similar marks may also appear on cherry or plum pits.

Owl pellets Undigested remains in owl pellets, which may contain bones or fur, can confirm the dormouse’s presence. Pellets are often found near human settlements, such as gardens or parking areas, as well as in forests.

Nests Woven from grass and leaves, hazel dormouse nests are typically hidden in dense shrubs like blackberry thickets. Roughly 8–15 cm wide with a small entrance, active nests should not be disturbed.

Sightings or physical evidence—such as nuts, pellets, or photographs—can be submitted at designated “nut stations” across Denmark or mailed to researchers using prepaid envelopes. Hansen encouraged families to participate, noting that even unsuccessful searches help children engage with nature.

“Finding traces of squirrels or wood mice still teaches them about the ecosystem,” she said. “But if we discover a new population, it would be incredible.”