The endangered common hamster needs proteins: identifying diversified crop-based diets improving hibernation and reproductive success.

Modern production-oriented farming has led to a decline in agricultural biodiversity. In Europe, one example of concern is the common hamster Cricetus cricetus, a hibernating rodent once largely distributed in farmlands and now listed as Critically Endangered. The decline of this species is tied to a significant decrease in hamsters' body mass at emergence from hibernation and in reproduction rate. Previous work has shown that monocultures of maize and wheat, which induce severe nutrient deficiencies, are a major cause of this phenomenon. To prevent such deficiencies, we tested in controlled conditions the effect of eight nutritive diets on hamsters' hibernation and reproduction. Diets were selected for their nutritional content and based on farmers' consultation. We tested three lipid-rich associations ('oat-sunflower', 'potato-sunflower' and 'buckwheat-sunflower'), two protein-rich associations ('maize-bean' and 'maize-pea') and an intermediate association ('wheat-soybean'), as well as 'sprouted wheat' and 'sugar beet'. Hamsters fed the lipid-rich diets showed a better body condition at the end of hibernation. However, a low reproductive success was recorded in all groups, with only 17% of reproductive trials leading to birth. Nonetheless, the amount of protein ingested by the mothers before reproduction increased birth probability whilst pups' survival to weaning was positively correlated to mothers' body condition. Overall, our results show that hamsters need a balanced diet to ensure their ability to reproduce. Indeed, low-protein diets led to lower birth rates and low-lipid diets led to reduced body condition and subsequently low pups' survival. The 'wheat-soybean' association best fulfilled hamsters' nutritional needs. Overall, these results highlight the need to improve current farming practices to provide a more fulfilling nutritional environment for common hamsters and the farmland fauna.