Individual variation in on-ice movement dynamics and site fidelity of western Hudson Bay polar bears
Creators: Jodouin, Camille
Publisher: name: University of Alberta Library
Year: 2023

<p>Individual variation affects fundamental aspects of ecology and behaviour in many species. Individuals vary in sex, age, reproductive status, and personality, which can be compared between individuals (inter-individual) or within individuals (intra-individual). In this dissertation, I tested whether individual variation affected various aspects of movement in polar bears (Ursus maritimus) of the western Hudson Bay subpopulation during the first and second halves of the ice season. In my first chapter, I examined whether intra-individual variation in age and reproductive status, as well as individual identity affected fidelity to on-ice areas in Hudson Bay. To this intent, I analysed differences in pairwise seasonal range centroid distance (as a proxy for broad-scale fidelity) and percent seasonal range overlap (as a proxy for fine-scale fidelity) of 87 collared adult females recaptured over multiple ice seasons in 2004-2021. Pairs of seasonal ranges had a mean centroid distance of 183 km (range 12 – 630 km, SE = 7 km), and overlapped on average by 12 %, (range 0 – 74 %, SE=0.01%), with 25% of pairs having zero overlap. Model selection revealed that broad-scale on-ice fidelity varied mainly by individual, suggesting possible differences in exploratory tendency between bears; however, there was no evidence of fine-scale fidelity in the western Hudson Bay population. In my second chapter, I investigated whether speed, path tortuosity, seasonal range size, and migration dates (i.e., on-ice departure and on-land arrival) differ as a function of sex and age, and individual identity. To do so, I used a combination of doppler-shift ear tag and GPS collar data from 110 bears, consisting of adult females with and without cubs, adult males and subadults captured in 2016-2021. Mean speed was 1.00 km/h (range 0.48 - 1.90 km/h, SE = 0.056 km/h) over all bears and was lower in adult males and females with offspring. My index of path tortuosity averaged 0.36 over all bears (range 0.042-0.90, SE=0.05; an index of 0 indicates an extremely tortuous path and an index of 1 indicates a perfectly straight path). Path tortuosity was lower in females with cubs-of-the-year and 2-year-olds. Overall mean seasonal range size was 22 000 km2 (range 1500 – 87 000 km2, SE=6400 km2), with males and subadults having significantly smaller seasonal ranges. Finally, bears departed onto the ice on average 7 days after sea ice freeze-up (range 1-20 days, SE=4.6 days) and arrived on land on average 38 days after sea ice break-up (range 14-55 days, SE=14.4 days). Migration dates did not differ by sex, age, or reproductive status. Each movement metric except for on-land arrival date also varied by individual bear, suggestive of differences in boldness levels, foraging strategies or physiology that possibly influenced individual movement. Each of my data chapters provides insights on how individual variation affects polar bear movement in western Hudson Bay and highlights the importance of including individual factors in polar bear movement research.  </p>