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DeBow, J., J. Blouin, E. Rosenblatt, K. Gieder, W. Cottrell, J. Murdoch, and T. Donovan. 2021. Effects of winter ticks and internal parasites on moose survival in Vermont, USA. Journal of Wildlife Management. DOI: 10.1002/jwmg.22101
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Abstract
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August 2021
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Moose (<i>Alces alces</i>) have experienced considerable declines along the periphery of their range in the northeastern United States. In Vermont, the population declined 45% from 2010 to 2017 despite minimal hunter harvest and adequate habitat. Similarly, nearby populations recently experienced epizootics characterized by >50% mortality. Declines have largely been associated with the effects of winter ticks (<i>Dermacentor albipictus</i>), but uncertainty exists about the effects of environmental and other parasite-related conditions on moose survival. We examined patterns of moose survival among a radio-collared population (<i>n</i> = 127) in Vermont from 2017 to 2019. Our objectives were to estimate causes of mortality and model survival probability as a function of individual and landscape variables for calves (<1 yr) and adults (≥1 yr). Observed adult survival was 90% in 2017, 84% in 2018, and 86% in 2019, and winter calf survival was 60% in 2017, 50% in 2018, and 37% in 2019. Winter tick infestation was the primary cause of mortality (91% of calves, 25% of adults), and 32% of all mortalities had evidence of meningeal worm (<i>Parelaphostrongylus tenuis</i>). Other sources of mortality such as vehicles, harvest, predation, deep snow, and other parasitic infections were negligible. The best supported calf model included sex differences and negative effects of tick engorgement (%/week) and parasite level (roundworm and lungworm). The best supported adult model included the effect of cumulative tick engorgement (cumulative %/week), which negatively affected survival. Our results indicate that winter tick engorgement strongly affects survival, and is probably compounded by the presence of meningeal worm and other parasites. Reduced tick effects may be achieved by decreasing moose density through harvest and managing late winter habitat to minimize tick density. Management of white-tailed deer (<i>Odocoileus virginianus</i>) density may also affect the transmission of meningeal worm.
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Blouin, J., J. DeBow, E. Rosenblatt, J. Hines, C. Alexander, K. Gieder, N. Fortin, J. Murdoch, and T. Donovan. 2021. Moose habitat selection and fitness consequences during two critical winter tick life stages in Vermont, USA. Frontiers in Ecology and Evolution 9:642276.
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May 2021
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Moose (<i>Alces Alces</i>) are a charismatic species that has been in decline across much of their southern range.<b> </b>In New England, USA, the reduction has been attributed, in part, to winter tick (<i>Dermacentor albipictus</i>) infestations. Winter ticks tend to be fairly immobile throughout all life stages, and therefore their distribution patterns at any given time are shaped largely by the occurrence of moose across the landscape during the peak of two critical time periods; fall questing (when ticks latch onto a moose, which coincides with the rut) and spring drop-off (when engorged female ticks detach from moose and lay their eggs in leaf litter). We used recent land cover and lidar data within a dynamic occupancy modeling framework to estimate first-order habitat selection (use vs non-use) of female moose (n = 74) during the questing and drop-off periods. Patch (1 km<sup>2</sup>) extinction and colonization rates during spring drop-off periods were strongly influenced by habitat and elevation, but these effects were diminished during the questing period when moose were more active across the landscape. In the spring drop-off period, patches where colonization was high and extinction low (highest probability of female moose occupancy) had higher proportions of young (shrub/forage) mixed forest at greater elevations. We evaluated the fitness consequences of individual-based habitat selection (second-order habitat selection) by comparing Resource Selection Functions (RSF) for 5 females that successfully reared a calf with 5 females whose calf perished. Second-order habitat selection analyses showed adult female moose whose offspring perished selected patches during the questing period that matched the first-order selection during the spring drop-off period. In contrast, adult female moose whose offspring survived selected areas with proportions of young deciduous habitats, as well as higher proportions of mature (canopy) evergreen forests and wetlands at lower elevations, i.e., their second-order habitat selection patterns deviated from the overall patterns illuminated by the multi-season occupancy analysis. Our model coefficients and mapped results define “hotspots” that are likely encouraging the deleterious effects of the tick-moose cycle. Knowledge about the composition and structure of these hotspots may influence more direct (i.e. hunter harvest) and indirect (i.e. conservation, modification, or formation of habitats) management decisions.
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Blouin, J., J. DeBow, E. Rosenblatt, C. Alexander, K. Gieder, J. Murdoch, and T. Donovan. Modeling moose habitat use by age, sex, and season in Vermont, USA using high-resolution lidar and National Land Cover data. Alces 57:71-98.
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September 2021
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Moose (<i>Alces alces</i>) populations have experienced unprecedented declines along the southern periphery of their range, including Vermont, USA. Habitat management may be used to improve the status of the population and health of individuals. To date, however, Vermont wildlife managers have been challenged to effectively use this important tool due to the lack of fine-scale information on moose space use and habitat characteristics. To assess habitat use, we combined more than 40,000 moose locations collected from radio-collared individuals (n = 74), recent land cover data, and high resolution, 3-dimensional lidar (light detection and ranging) data to develop Resource Utilization Functions (RUF) by age (mature and young adult), season (dormant and growth), and sex. Each RUF linked home range use to average habitat conditions within 400 m or 1 km of each 30 m2pixel within the home range. Across analyses, the top RUF models included both composition (as measured through the National Land Cover Database) and structure (as measured through lidar) variables, and significantly outperformed models that excluded lidar variables. These findings support the notion that lidar is an effective tool for improving the ability of models to estimate patterns of habitat use, especially for larger bodied mammals. Generally speaking, female moose actively used areas with proportionally more regenerating forest (i.e., forage < 3.0 m) and more mature forest (i.e., canopy structure > 6.0 m), while males actively used more high elevation, mixed forest types. Further, moose exhibited important seasonal differences in habitat use that likely reflect temporal changes in energetic and nutritional requirements and behavior across the year. Moose used areas with proportionally more regenerating forest (i.e., forage < 3.0 m) during the growth period and female moose had strong positive associations with lidar-derived canopy structure during the growth (but not the dormant) period. Ultimately, the resultant maps of habitat use provide a means of informing management activities (e.g., the restoration or alteration of habitats to benefit moose) and policies around land use that may contribute to population recovery.
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