Date of Award
Program or Major
Master of Science
Russell G Congalton
High calf mortality has been documented in North American moose (Alces alces) populations along the southern extent of their range; in New England, this has been attributed to winter tick (Dermacentor albipictus) parasitism. This research was conducted to better understand moose activity during critical periods in the winter tick life cycle, and to assess the potential of simulation models in managing moose against future epizootics. Seasonal habitat use was measured using geospatial analyses of locational data from radio-marked animals at 3 sites in New Hampshire and Maine. An agent-based model, spatially explicit to two subsections of the New Hampshire field site (Success and Jericho), was then constructed to simulate the role of moose density, weather events, winter tick abundance and aggregation, and proportion of available optimal habitat on % mortality and tick infestation level of dead calves.
The average size of home and core ranges generally increased from south to north, following the population gradient. Optimal habitat was the only land cover type used above its availability (1.1-2.1X availability in home range, 1.2-3.1X availability in core range), regardless of season or site, indicating that moose were selecting for this cover type during questing and drop-off periods of winter ticks. The proportional overlap of cut habitat in home and core ranges exceeded the absolute proportion in home and core ranges. It is expected that temporal use of optimal habitat exceeds the geospatial estimates because 30-40% of the daily activity of moose is spent foraging. The high proportion of time spent foraging within optimal habitat that is available in disproportionately low proportion (< 20%) across the landscape suggests that high concentrations of winter ticks are available in this cover type.
The model was parameterized using empirical data acquired from the literature and results of the current field study. Of 58 combinations of variables, 17 produced epizootic events (calf mortality > 50%), of which 15 occurred in Jericho where the availability of optimal habitat was higher (28%) than the study site average (17%). Averages of the two sites under conditions representative of the current moose density and recent weather conditions yielded similar, albeit lower, calf mortality (53-66%) and infestation level (37,635 ticks/calf) than measured in the field study (~70% calf mortality, 48,600 ticks/calf). Winter tick abundance and aggregation both influenced the occurrence and severity of infestation and mortality at each site. While the model used a conservative approach with regard to several parameters (e.g., moose activity, winter tick abundance, % ticks that desiccate during drought, and moose density), it produced patterns and trends congruent with those calculated during the field study, and demonstrated the future management potential of this method.
Healy, Christine, "MOOSE HABITAT USE DURING CRITICAL PERIODS IN THE WINTER TICK LIFECYCLE AND AGENT-BASED MODELING OF MOOSE-WINTER TICK RELATIONSHIPS IN NORTHERN NEW HAMPSHIRE" (2018). Master's Theses and Capstones. 1205.