Defining biologically relevant seasons is a critical issue in the interpretation of animal space-use studies. Moreover, understanding the effects of extrinsic (e.g., predation risk) and intrinsic (e.g., age and sex) factors on individual differences in seasonal transition dates will deepen our understanding of the mechanisms driving animal movement and potentially population dynamics. We used nonlinear modeling of movement rate over time using global positioning system–collared nonmigratory elk (Cervus elaphus manitobensis) and white-tailed deer (Odocoileus virginianus) in southern Manitoba, Canada, to derive species- and sex-specific seasonal transition dates. In addition, we used variables known to influence timing of migration in migratory populations to explain individual differences in seasonal transition dates. We found ecologically important differences in start and length of seasons between male and female elk and white-tailed deer. Individual differences in seasonal transition dates were large, and could be explained by a combination of intrinsic and extrinsic factors. Age-class of the individual animal and elevation influenced timing of winter, spring, and date of parturition, whereas predation risk from wolves (Canis lupus) influenced onset of spring, summer, and autumn. Our findings suggest that similar extrinsic and intrinsic factors can influence both large- (i.e., migratory) and small-scale movement patterns and can be used effectively to empirically define biologically relevant seasons for sympatric large herbivores.