Was everything better in the good old days? Declining body mass in the Garden Dormouse (Eliomys quercinus)

Garden Dormouse ( Eliomys quercinus ) populations have shown a drastic decline over the last 20-30 years, reasons for this are still unknown. In wild animals, body mass is good indicator of fitness and survival probability, especially in hibernating species like dormice. Fat accumulation before onset hibernation juvenile growth crucial to survive following winter. We conducted capture-mark-recapture study Black Forest (south-western Germany) between 2018 2021 compared captured Dormice with data collected 2003 2005. Furthermore, we investigated dietary spectrum by faecal analyses. The results show that adult nowadays significantly lower (difference 11 ± 2.8 g) than two decades ago. juveniles showed gain years 2018-2021 2003-2005. Dietary analyses revealed insects represent main food resource also adults during pre-hibernation fattening. This shows, has decreased decades, which could reduce their reproductive success rate, hibernation. A reason reduction be severe leading an insufficient availability key species. particular, females might not able cover investment gestation lactation.