Intra-seasonal Shifts in Summer Elk Diet Composition

Elk (Cervus canadensis) require adequate forage to fulfill their seasonal nutritional requirements. Elk undergo their highest nutritional demands during summer to support critical life functions such as late gestation, lactation, and juvenile growth. During this period, variations in plant phenology significantly influence the quality and quantity of forage on the landscape. Recent literature has concentrated on late summer due to it's limiting nature. Yet, growing evidence suggests that both early and late summer forage often fail to meet the nutritional demands of lactating and reproducing female elk. Further, there is limited knowledge surrounding the intra-seasonal dynamics of elk diet composition during summer. To address this, we utilized data from two elk populations in Montana (Noxon and Blackfoot study areas) to examine how phenology and availability drove changes in elk diet composition between early and late summer. We determined diet composition using DNA metabarcoding of fecal samples, then used Principal Component Analyses (PCA) to examine the changes in elk diet over time. Our results indicate that late summer diets had less variability than early summer diets in both study areas. In the Noxon study area, elk diets varied intra-seasonally and were mostly driven by changes in forage phenology. Conversely, elk diets in the Blackfoot study area did not change significantly between early and late summer due to influences related to both phenology and availability. Our findings work to enhance the understanding of elk forage utilization throughout the entire course of summer, providing background to inform habitat management approaches during a critical season for elk.