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Many wildlife populations are experiencing a variety of environmental pressures due to the direct and indirect consequences of a changing climate. In the northeast, USA, moose Alces alces are declining in large part because of the increasing parasitism by winter tick Dermacentor albipictus, facilitated by high host density and optimal environmental conditions. To test this hypothesis, and better understand the influence of this interaction on the stability of the regional population, we constructed a population viability model using data collected through comprehensive survival and productivity studies in 2002–2005 and 2014–2018 in northern New Hampshire. Years of heavy tick infestation (epizootics) saw a marked reduction in calf survival (< 50%), adult calving (< 60%), twinning rate (< 5%) and complete loss of yearling productivity. We conducted population viability analysis using VORTEX ver. 10.2 to model this moose population for 40 years using mean demographics from both time periods, including environmental variation measured in the field during winter tick epizootic (2002, 2014, 2015, 2016) and non-epizootic (2003, 2004, 2005, 2017) years. This exercise highlights the influence of winter tick infestation on the trajectory of the population with the potential for rapid population growth or decline depending on the frequency of epizootics. We suggest a shift in moose management strategy focused on lowering moose density, assuming continued influence of climate change on the host–parasite relationship. [ABSTRACT FROM AUTHOR]

Moose (AIces alces) are susceptible to late winter mortality from infestation of winter ticks (Dermacentor albipictus) throughout much of North America. Calves, perhaps more so than other ages of moose, likely experience chronic, and eventually acute anemia from blood removal by adult female ticks that peaks during weeks 4 - 6 of the 8-week engorgement period. We modeled the potential metabolic impact on protein and energy balance of moose calves associated with blood loss during four levels, low to severe, of winter tick infestation. Our conservative estimates indicated that total blood loss in weeks 4 - 6, as a percent of total blood volume, ranged from 27 to 48% and 64 to 112% during moderate (30,000 ticks) and severe (70,000 ticks) infestations, respectively. The percent of the daily metabolizable energy requirement needed to replace daily blood loss during weeks 4 - 6 was 4.9- 8.2% and 11.4 - 19.2% during moderate and severe infestations, respectively. The protein deficit associated with blood loss and regeneration was the most critical metabolic impact. Daily protein loss during weeks 4 - 6 was 29 - 49% and 68 - 114% of the daily protein requirement in moderate and severe infestations, respectively. Daily protein losses of ∼ 30 to > 100% occurred for 2 continuous weeks. Energy costs associated with compensating for blood loss would likely elevate the daily energy deficit normal at end of winter, accelerate nutritional decline and weight loss, and cause increased physiological stress related to concurrent anemia. Severely infested calves are obviously susceptible to late winter mortality, and the impact of moderate infestations would be exacerbated by secondary parasitic infestations, severe winters, and poor body condition. [ABSTRACT FROM AUTHOR]