Is winter diet quality related to body condition of white-tailed deer (Odocoileus virginianus)? An experiment using urine profiles

Abstract

During winter, boreal forest herbivores have access to only poor-quality forage. On Anticosti Island (Quebec, Canada), the ongoing reduction of balsam fir (Abies balsamea (L.) P. Mill.) owing to overbrowsing by white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)) may force deer to include a higher proportion of white spruce (Picea glauca (Moench) Voss), a browse normally avoided, in their winter diet. We tested the hypotheses that (i) deer body condition during winter and (ii) the costs of detoxification of plant secondary metabolites in the winter diet could be estimated by monitoring the 3-methylhistidine / creatinine and glucuronic acid / creatinine ratios, respectively, in urine collected in snow from white-tailed deer fawns. Doubling the amount of white spruce in the winter diet of deer (from the current 20% under natural conditions to 40%) did not increase 3-methylhistidine / creatinine ratios but increased the glucuronic acid / creatinine ratio in urine, suggesting that a diet containing more spruce was more toxic. A weak positive relationship was observed between 3-methylhistidine and percent cumulative mass loss. There was no relationship between the 3-methylhistidine / creatinine ratio and the number of days left before death, as well as no relationship between the ratio of glucuronic acid / creatinine and percent cumulative mass loss. We conclude that the costs of detoxification of plant secondary metabolites in the winter diet of white-tailed deer in boreal forests could be monitored with glucuronic acid / creatinine ratios, but that 3-methylhistidine / creatinine ratios were weak indicators of deer body condition in winter.