Search

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]

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]

Abundance indices suggested that the moose Alces alces population in northern New Hampshire was stable despite favourable habitat and conservative harvest. Causes and rates of mortality were unknown because moose reproduction and survival was unstudied in the region. Our study was designed to investigate the dynamics of the regional population in 2002-2005.Atotal of 92 moose (33 cows and 59 calves) were captured and fitted with radio-collars (VHF=83, GPS= 9). Parturition ranged from 8 May to 13 July (median = 19 May) with 78% of births occurring during 13-27 May. Calving rate of yearlings and adults (>2 years old) averaged 30 and 85%, respectively; twinning rate was 11%. Analysis of reproductive data from harvested cows (1988-2004) indicated that the average weight of adult cows increased but their corpora lutea count declined from ; 1.4 to 1.2/cow. Both ovulation rate and average weight of yearling cows declined about 25 and 4%, respectively. There were 39 mortalities (49% calves) with winterkill/parasite (41%), vehicle collision (26%) and hunting (18%) as the leading causes. Major sources of mortality of radio-marked cows were human-related; survival was 0.87. Annual calf survival was 0.45. Unmarked calf (0-2 months of age) survival was 0.71 with 76% of mortality in the first month of life. Radio-marked calves (∼7-12 months of age) had a survival rate of 0.67; 74% of the mortality was winterkill/parasite related. Calf mortality was concentrated (88%) in late winter-early spring. The unseasonably warm and snowless fall in 2001 probably favoured high tick transmission and increased tick loads on moose that resulted in high calf mortality (0.51) and measurable cow mortality (10%) in mild winter-spring 2002. Documentation of substantial tick-related mortality of radio-marked moose calves was unique to this study. The stability of the moose population probably reflects the variation in annual recruitment and lower fecundity of yearling cows associated with heavy infestations and epizootics of winter tick. Given that fertility, calving rate and body condition of adult cows, and summer calf survival are annually high, the population should recover from tick epizootics that periodically inhibit population growth. [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]