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.
Abstract
Moose (Alces Alces) are a charismatic species that has been in decline across much of their southern range. In New England, USA, the reduction has been attributed, in part, to winter tick (Dermacentor albipictus) 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 km2) 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.