The Role of Forage Quantity and Quality in the Migration and Diet of a Northern Ungulate During Their Neonatal Period

ABSTRACT Migration has evolved as a strategy to maximize survival and reproductive success, driven by the search for better resources and/or predator avoidance. For ungulates at high latitudes, the search for higher quality and more abundant forage has been proposed as one of the best explanations of seasonal migrations. However, responses vary among populations, species, and ecosystems. In this study, we examine the forage resources associated with an annual migration of a herd of wood bison ( Bison bison athabascae ) in northeast Alberta, Canada. Timing of this migration corresponds to the neonatal period in late spring during green up when females have a higher nutritional demand imposed by gestation and maternal care of neonates. The objective of this work was to assess how forage quantity (i.e., biomass) and quality (i.e., crude protein and metabolizable energy, ME) differed between the herd's core and neonatal ranges while evaluating differences in their diet. Bison diets during winter in the core range were dominated by graminoids and shrubs, while shrubs and forbs were predominant in diets within the neonatal range from late spring through summer. Overall, the neonatal range during spring had significantly greater biomass ( p < 0.001) of shrubs and forbs compared with the core range during the same season, being 1.7 and 3.8 times higher, respectively. The neonatal range also had comparatively more crude protein and ME ( p < 0.001) during this season, with crude protein being 2.7 and 3.2 and ME being 3.0 and 3.7 times greater than in the core range for shrubs and forbs, respectively. Conversely, the core range had higher biomass, crude protein, and ME ( p < 0.001) available for graminoids compared with the neonatal range during spring. However, graminoids are not particularly common in their diet during the migration period. Our results suggest that bison migration to the neonatal range, coincident with higher quantity and quality of forage, is important for female wood bison, particularly given their increased post‐parturition demands for energy and protein during this critical neonatal period.