Seasonal breeding in relation to dietary animal protein in deer mice (Peromyscus maniculatus)

We used stable carbon and nitrogen isotope compositions of hair and liver as a way of examining seasonal diet changes and explaining seasonal breeding in deer mice ( Peromyscus maniculatus (Wagner, 1845)). Summer and winter δ13C values differed, which is attributed to the availability of different plant tissues (C3 plants). The δ15N values of liver showed a decrease in consumed animal protein during winter, but the difference was not large enough to indicate a full trophic level change in diet from summer to winter. The δ15N values of hair remained constant across the seasons, which is attributed to a continuous level of moulting throughout the year. Our data indicate that lowered food quality in the form of reduced dietary animal protein intake may play a role in the cessation of breeding in deer mice in winter.