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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 alcesare 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.

Energetic models which incorporate environmental measures have demonstrated that significant thermoregulatory savings are accrued from nocturnal winter roost-sites, usually from reduced wind speed and radiated heat loss. Because blue grouse Dendragapus obscurusoccupy high elevation, snowbound coniferous stands in the Rocky Mountains during winter, selection of a favourable microhabitat is likely their primary thermoregulatory behaviour. Therefore, we measured the microclimatic conditions at diurnal and nocturnal roost-sites of blue grouse to determine whether their choice of roost-sites reflects thermoregulatory behaviour. Temperature, wind speed, and solar radiation were measured at 17 diurnal Douglas-fir Pseudotsuga menziesiiand 17 nocturnal subalpine fir Abies lasiocarparoost-sites and compared to those of an open control site in Logan, Utah, 1985–1986. Temperature varied <2°C between the roost-sites and the control site. Wind speed was significantly lower in 15 of 17 diurnal ( = 0.71 m/sec) and all nocturnal roost-sites ( = 0.24 m/sec) than in the control site ( = 1.75 m/sec). Wind speed was reduced >75% at all but one nocturnal roost-site. Solar radiation at the diurnal roost-sites ( = 51 W/m-2) was significantly lower than at the control site (201 W/m-2); however, five roost-sites had maximum values >90% of the control maximum. Douglas-fir roost-sites had significantly greater solar radiation, diurnal, and nocturnal wind speed than subalpine fir roost-sites. Reduction of convective heat loss was the major thermoregulatory contribution of both diurnal and nocturnal roostsites. Diurnal roost-sites also afforded measurable radiant energy and, presumably, grouse could track the sun in roost trees to maximize such heat input. Daily energy costs predicted from metabolic equations incorporating temperature and wind speed were below the metabolizable energy intake of captive blue grouse. Application of the average microclimatic conditions from both roost trees to an energetic model revealed that a blue grouse would realize a 50% greater reduction in convective heat loss, and a 10% greater net energy savings, by roosting overnight in a subalpine fir rather than a Douglas-fir. This difference may explain why blue grouse show affinity to subalpine firs for nocturnal roosting, and points to the energetic importance of specific coniferous habitats to wintering blue grouse.