Extinction lurks for a flagship species in agricultural habitat: three years of supplementation of the common hamster in Belgium

The first common hamster Cricetus cricetus species protection program in Belgium was conducted between 2015 and 2021. Within this Flemish government program, annual introductions of captive-bred hamsters into the population in Widooie (Tongeren) occurred from 2019 to the present. Monitoring of motion, survival, habitat selection, and reproductive parameters of introduced individuals was carried out to evaluate the success of the conservation actions. Remote sensing techniques; specifically, VHF transmitters, camera traps, and desktop spatial analyses, were used during 3 consecutive years to acquire and analyze data from 52 introduced hamsters (12 males, 40 females). The overall survival rate of introduced males in the first months after introduction (75.00% after the first month, which dropped to 8.33% by the end of the third month) was significantly lower than findings from other studies. We identified a lack of local optimal habitat with connecting elements as a possible driver for this reduced survival. The reproductive data showed that the introduced females in Widooie produced a limited number of litters in a season. Also, the median number [IQR] of pups per litter 1 [1-2] is too low to keep the population size of this prey species at a stable population level. We hypothesize that the females cannot consume enough animal and/or plant proteins before and during the reproductive period, which could endanger pregnancy, lactation, and thus litter size. Failing to address the declining reproductive rate in the wild poses a substantial threat to the conservation of endangered hamster populations.