• Seasonal variation in nutritional biomarkers and fecal cortisol concentrations in a northern population of snowshoe hares

      Montgomerie, Claire Kornet; Kielland, Knut; Breed, Greg; Lian, Marianne (2020-08)
      Blood biomarkers indicative of nutritional status, fecal cortisol metabolite concentrations and an established body condition index (BCI), were collectively examined from snowshoe hares(Lepus americanus) inhabiting northern Alaska in 2018, during five ecologically significant times of year. As a novel approach to increase our understanding of the effects of diet and predation pressure on hare physiology, I addressed how these markers were associated with seasonal timing of energetic demands and adult survival rates. Mean decreases in concentrations of total protein (TP), blood urea nitrogen (BUN), hematocrit (HCT) and glucose during spring and autumn, suggest that snowshoe hare nutritional status decreased during these two seasons in 2018. The shoulder seasons of spring and autumn coincide with energetic challenges, including molt, changes in diet and breeding. Because available forage during these seasons largely consists of winter-dormant twigs, the energy expenditure of growing a new winter coat (autumn) and breeding behavior (spring) may compromise the energy balance of hares during these periods. Male hares, whose activity levels increase during breeding, exhibited lower BCI scores and were slower to molt from white to brown than female hares in May. Furthermore, adult survival rates were lowest during spring months. Snowshoe hare mean fecal cortisol metabolite concentrations did not show associations with seasons of apparent low nutritional status. Adult hare survival rates peaked during summer and early autumn, during which mean values of TP, BUN, Hct, Cl (chloride), Na (sodium) and glucose also increased. By contrast, this period coincided with a 2-fold increase in mean fecal cortisol metabolite concentrations, suggesting that the apparent stressor was not related to nutrition. Interestingly, after having decreased in autumn, BUN, Hct, TP, and glucose mean concentrations increased in midwinter. Free calcium (iCa) and potassium (K) mean concentrations were also highest in December. Hares may have reduced activity during winter months, and metabolic rates may have increased to cope with thermoregulation demands. BCI scores decreased by December, suggesting use of endogenous reserves. Lowest seasonal mean cortisol metabolite concentrations were also observed in mid-winter. This study demonstrates the value of examining both physiological and morphological metrics of snowshoe hare condition to better our understanding of how seasonal trends in food and fear may unfold into cyclic patterns.