Data and code from: The role of forage quantity and quality in the migration and diet of a northern ungulate during their neonatal period

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 to 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.