Shifting seasonality of annual growth through ontogeny for red deer at northern latitudes

Large mammals at northern latitudes show annual cycles of body mass gain insummer and body mass loss in winter. The amplitude and seasonal timing ofthese cycles may vary through ontogeny depending on trade-offs towardinvestments in structural growth versus fat storage, reproduction, and futuresurvival. Despite this knowledge, there is no detailed model of how the season-ality of body mass develops through ontogeny. Here, we define a new seasonalgrowth model that accounts for shifting seasonality through two sine compo-nents: one included in the growth coefficient and the other on the asymptoticsize. We fitted 12 candidate models to longitudinal data on body mass of cap-tive male and female red deer (Cervus elaphus) in Norway, with different base-line growth structures (von Bertalanffy, Gompertz, and Brody) and includingzero, one, or both of the seasonal components. The best fitting model was theBrody model with both seasonal components included, allowing the annualpeak to shift through ontogeny: The annual peak occurred in December forcalves, shifting to November in yearlings, and October in 2- and 3-year-olds,ending with September for adults. All age classes showed an annual minimumat the end of winter around March. Males and females showed similar sea-sonal peaks through ontogeny, although males grow bigger and have largerseasonal amplitudes. Our new growth model provides a flexible framework tomodel seasonal growth changing through ontogeny, applicable to differentspecies. Brody, Gompertz, growth model, ontogenetic shift, red deer, seasonal growth, seasonality,ungulates, von Bertalanffy