Covariates of Intraspecific Variation in Hibernation Expression in the Northernmost Population of Black-tailed Prairie Dogs

Hibernation is an energy-saving strategy employed by species to survive periods of low resource abundance and inclement weather. Due to the costs and benefits associated with the use of torpor and arousal during hibernation, individuals are predicted to hibernate according to their energetic state entering hibernation and their requirements following hibernation. The timing and quantity of energetic requirements following hibernation can vary between the sexes due to differences in selective pressures. Thus, there is potential for sexual variation in hibernation expression to exist. Species and/or populations that exhibit individual variation in hibernation expression lend themselves as an ideal species to test such predictions. \n\nBlack-tailed prairie dogs (Cynomys ludovicianus) are a species that demonstrates tremendous variation in over-winter thermoregulatory strategies across their range. Prairie dogs within Canada comprise the northernmost population of this species and are the only population of black-tailed prairie dogs known to consistently hibernate over winter. Previous studies reveal variation in hibernation expression within this population. Yet, it is currently unknown what influences this variation, and in general, this unique aspect of their biology remains understudied. However, recent study indicates that males and females differ in their overwinter winter mass loss which may result from differences in hibernation expression.\n\nIn this thesis, I investigated the role of sex and pre-hibernation body condition on hibernation expression and over-winter energy expenditure in a single colony of prairie dogs located in Grasslands National Park, SK, CA. First, I investigated whether males and females differed in their hibernation expression and energy expenditure by assessing the use of various hibernation traits and quantifying over-winter change in body condition. I found that females had longer hibernation periods, used more bouts of torpor, and overall spent a greater amount of time in torpor compared to males. However, males spent a greater proportion of their shorter hibernation period in torpor and used longer, colder bouts of torpor. Despite differences in hibernation expression, I did not find any evidence that males and females lost similar amounts of condition over winter, though males appeared to lose condition at a faster rate. However, results regarding over-winter changes in body condition should be interpreted with caution due to discrepancies between when male and female prairie dogs hibernated relative to when I recorded body condition measurements.\n\nI also conducted a supplemental feeding trial during a portion of the pre-hibernation fattening period of prairie dogs to expand variation in pre-hibernation body condition and combined this data with previously existing data to investigate the influence of pre-hibernation body condition on hibernation expression and over-winter change in body condition. I found that, relative to individuals in poor condition, individuals in better pre-hibernation body condition did not shorten the duration of the hibernation period but did reduce the proportion of the hibernation period spent torpid and increased the length of arousal bouts. Prairie dogs in good pre-hibernation body condition did experience a greater decrease in body condition over winter but still emerged from hibernation in better condition compared to individuals of a poorer condition.\n\nThe work presented in this thesis increases our understanding of a relatively unknown aspect of black-tailed prairie dog biology - hibernation. Additionally, this thesis improves our understanding of the factors that influence hibernation expression and how individuals alter their use of hibernation with respect to their energetic condition. Future research investigating prairie dog body mass dynamics immediately after hibernation and the effects of sociality and predation on hibernation could be explored to further our understanding of hibernation use. Increasing our understanding of the factors that influence intraspecific variation in hibernation expression can lead to advances in understanding how hibernation evolved as well as aid us in our predictions of if and how populations will respond to changing environments.

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