Year of Award
Thesis - Campus Access Only
Master of Science (MS)
Department or School/College
College of Forestry and Conservation
Daniel Pletscher, Evelyn Merrill, Joel Berger
Adult Female Survival, Behavior, Elk, Partial Migration
University of Montana
Within a migratory species, individuals that migrate are expected to enhance lifetime fitness through exposure to higher quality forage and avoiding predation to a greater degree than non-migratory conspecifics. Partial migration occurs when a portion of the population migrates and the other portion remains on the shared range, and is expected to be maintained by balancing fitness between migrant and resident phenotypes. Most previous research treats partial migration as a definitive phenomenon with discrete migrant or resident phenotypes. However, recent studies acknowledge that ungulate migration may be variable and occur along a gradient between end points. We first tested variability in individual migratory behavior using a ten-year VHF and GPS telemetry dataset of 223 adult female elk (Cervus elaphus) in the declining Ya Ha Tinda partially migratory population in west-central Alberta, Canada. We used measures of net squared displacement (NSD) from the winter range, plotted over time in combination with a Global Information System (GIS) to quantify movements. We found that individuals switched between migrant and resident strategies at a mean rate of 15%/year, ~10% of the population used an intermediate migratory strategy with both resident and migratory characteristics, and density-dependent switching such that at higher winter densities, elk switched from resident to migrant, whereas at lower densities, elk reversed direction. This evidence for flexibility in migration supports the idea of behavioral plasticity in migration. Next, we tested for density dependence in adult female survival and cause-specific mortality rates, as well as differences between migrant and resident elk in this population. We used Kaplan-Meier estimates of survival, tested for factors affecting survival using Cox-proportional hazards models, and for density-dependence in predation rates using Cumulative Incidence Functions. We found weak evidence of annual measures of negative density dependence in survival and cause-specific mortality in regulating migrant and resident elk, and few differences between strategies in either survival rates or overall predation rates, suggesting equal payoffs between strategies in this declining elk population. The constant predation rate across the study support the continued decline in population size and suggest that elk in this population were limited by density independent predation because of no predator-based carrying capacity. This is perhaps due to alternate prey within the system and behaviorally-based balancing of survival between migratory strategies.
Eggeman, Scott, "Migratory Behavior and Survival of Adult Female Elk in a Partially Migratory Population" (2012). Graduate Student Theses, Dissertations, & Professional Papers. 663.
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© Copyright 2012 Scott Eggeman