Moose Habitat Selection and Fitness Consequences During Two Critical Winter Tick Life Stages in Vermont, United States†

Abstract

The moose (Alces alces) is a charismatic species in decline across much of their southern distribution in North America. In the northeastern United States, much of the reduction has been attributed to winter tick (Dermacentor albipictus) infestations. Winter ticks are 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 moose) and spring drop-off (when engorged female ticks detach from moose). 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 tick questing and drop-off periods. Patch extinction and colonization rates between the fall questing and spring drop-off periods were strongly influenced by habitat and elevation, but these effects were diminished during the fall questing period when moose were more active across the landscape. From the fall questing period to the spring drop-off period, patches where colonization was high and extinction was low had higher proportions of young (shrub/forage) mixed forest at higher elevations. Further, we evaluated the fitness consequences of habitat selection by adult females during the fall questing period, when females and their calves acquire ticks. We compared Resource Selection Functions (RSF) for five females that successfully reared a calf to age 1 with five females whose calves perished due to ticks. Adult female moose whose offspring perished selected habitats in the fall that spatially coincided with areas of high occupancy probability during the spring tick drop-off period. In contrast, adult female moose whose offspring survived selected areas where the probability of occupancy during the spring drop-off was low; at present, natural selection may favor female adults who do not select the same habitats in fall as in spring. Our model coefficients and mapped results define “hotspots” that are likely encouraging the deleterious effects of the tick-moose cycle. These findings fill knowledge gaps about moose habitat selection that may improve the effectiveness of management aimed at reversing declining population trends.

Managing Moose from Home: Determining Landscape Carrying Capacity for Alces alces Using Remote Sensing

“…Additionally, the temporal flexibility allows prediction of the impacts of recent timber harvest on an annual basis or to periodically evaluate landscape changes when setting long-term management objectives [32]. Recent approaches have utilized LiDAR to create more comprehensive forest cover predictions that can identify more subtle variations in stand structure [51,62,63], but LiDAR can be cost prohibitive when predicting forest cover at large spatial scales or at multiple points in time [12].…”

Advances in wildlife abundance estimation using pedigree reconstruction

“…Individuals in our simulated population were assigned random home range centroids within the study area using the spsample() function in the sp package (Bivand et al., 2013 ; Pebesma & Bivand, 2005 ). We assigned locations based on global positioning system (GPS) collar data collected on moose of the same sex and age in the study area, adjusted to be relative to each simulated animal's home range centroid (Blouin et al., 2021a , 2021b ). Animal centroids would change as individuals dispersed, and location data would be updated as individuals aged into older age classes.…”

“…Low-density moose populations exist along the southern edge of the species distribution in eastern North America. Suitable habitat for these moose population are often known (e.g., Blouin et al, 2021aBlouin et al, , 2021b and could inform spatially based sampling for pedigree reconstruction and aid in the monitoring of low-density populations.…”

Warm places, warm years, and warm seasons increase parasitizing of moose by winter ticks

“…In this suite of models, we considered relative moose density (Bergeron & Pekins, 2014;Samuel, 2007), spatial overlap on winter range shared with other ungulates (deer [Odocoileus spp. ] or elk [Cervus elaphus]) that could serve as additional hosts (Welch et al, 1991), vegetation type (Addison et al, 2016;Drew & Samuel, 1986;Healy et al, 2018;Powers & Pekins, 2020), and individual moose migratory behavior (Blouin et al, 2021;Healy et al, 2018; Table 2). We characterized vegetation type at each capture site according to year-specific land cover data using the International Geosphere Biosphere Programme (IGBP) global vegetation classification of the moderate resolution imaging spectroradiometer (MODIS) land cover product (MCD12Q1) at a 500 × 500 m resolution, following Liang et al (2015).…”