Migration is typically thought to be an evolved trait driven by responses to forage or predation, but recent studies have demonstrated avoidance of parasitism can also affect success of migratory tactics within a population. We evaluated hypotheses of how migration alters parasite exposure in a partially migratory elk (Cervus canadensis) population in and adjacent to Banff National Park, Alberta, Canada. Equal numbers of elk remain year-round on the winter range or migrate to summer range. We quantified diversity and abundance of parasites in faecal elk pellets, and prevalence (number of infected individuals) and intensity (egg counts) of giant liver fluke eggs (Fascioloides magna) in faeces across migratory tactics. We tested whether giant liver fluke intensity in faeces was affected by elk use of wetlands, elevation, forage biomass, and elk concentration in the previous summer. We rejected the “migratory escape” hypothesis that suggests migration allowed elk to escape parasite exposure because migrant elk had the highest richness and evenness of parasite groups. We also rejected the hypothesis that prevalence was highest at highest summer densities because higher-density resident elk had the lowest diversity and giant liver fluke egg presence and intensity. Instead, the high prevalence and intensity of giant liver flukes in migrants was consistent with both the hypothesis of “environmental tracking”, because elk that migrated earlier may expose themselves to favourable parasite conditions, and with the “environmental sampling” hypothesis, because giant liver fluke intensity increased with increased exposure to secondary host habitat (i.e., wetland). Our results indicate that differential exposure of different migratory tactics that leave the winter range has a greater influence on parasites than the concentration of elk that reside on the winter range year-round.

通常认为迁移是由对草料或掠食的反应驱动的进化特征，但是最近的研究表明，避免寄生虫也可能影响种群内迁徙策略的成功。我们评估了迁移如何改变加拿大艾伯塔省班夫国家公园及其附近部分迁徙的麋鹿（加拿大鹿）种群中寄生虫暴露的假说。在冬季范围内，全年都有相同数量的麋鹿，或在夏季范围内迁移。我们量化了粪便麋鹿颗粒中寄生虫的多样性和丰度，以及巨大的肝吸虫卵（Fascioloides magna）的患病率（感染个体数量）和强度（卵数））在各种迁移策略中的粪便中。我们测试了粪便中巨大的肝吸虫强度是否受到前一年夏季麋鹿对湿地的使用，海拔，饲料生物量和麋鹿浓度的影响。我们拒绝了“迁移逃逸”假说，该假说认为迁移使麋鹿逃脱了寄生虫暴露，因为移民麋鹿具有最高的寄生虫群体丰富度和均匀性。我们还拒绝了这样的假设，即夏季密度最高时患病率最高，因为密度较高的常驻麋鹿具有最低的多样性，并且巨吸虫卵的存在和强度。取而代之的是，移民中巨大的肝吸虫流行率和强度都与“环境追踪”假说相吻合，因为迁徙较早的麋鹿可能会处于有利的寄生虫条件下，并采用“环境采样”假说，因为巨大的肝吸虫强度随着对次生寄主生境（即湿地）的接触而增加。我们的结果表明，离开整个冬季范围的不同迁徙策略的差异暴露对寄生虫的影响大于全年常驻冬季范围内麋鹿的浓度。