Summer spatial ecology of woodland caribou across northern Ontario

  • Author / Creator
    Walker, Philip
  • Caribou (Rangifer tarandus) numbers continue to decline across their circumpolar range with boreal woodland caribou (R. t. caribou; hereafter caribou) listed as threatened under Canada’s Species at Risk Act. Given this conservation concern, evaluating the factors influencing reproductive success of caribou is key to developing management strategies. Survival of adult females and their calves is a function of behavioural responses that individuals make across varying spatiotemporal conditions. I evaluated calving behaviours of female caribou across three northern Ontario study regions (Pickle Lake, Nakina, and Cochrane). I first identified caribou parturition and 5-week neonatal mortality using a movement-based approach, which was validated based on footage from 22 video-collared caribou. Across regions, 76% of 107 caribou-years indicated birth events with differences in median birth date of one week later in Cochrane (23 May) than in Pickle Lake (17 May) and Nakina (16 May), which indicate possible phenological differences due to greater overwinter snow in Cochrane. Seventy percent of females that gave birth maintained their calf through the first 5-weeks postpartum, with higher risk of neonatal mortality associated with use of lowlands and greater postpartum movement rates. The ability to identify parturition and calf survival led me to propose that individual caribou may use different strategies in expressing spatial (use of same location) or habitat fidelity (use of same habitat) during calving to maximize reproduction. I identified 56 individuals with >2 predicted birth events, and compared the types of fidelity expressed (i.e., spatial, habitat, or no fidelity) to caribou age, calf survival, and habitat quality and predictability in calving ranges. Across all caribou, 36% expressed no fidelity, 29% expressed spatial fidelity, 50% expressed habitat fidelity, and 14% expressed both habitat and spatial fidelity, where older individuals were more likely to express spatial fidelity and caribou in areas of lower habitat quality increased the probability of expressing habitat fidelity. Fidelity type did not influence calf survival, but the sample size was small.

    Due to differences in body fat and pregnancy rates between Pickle Lake and Cochrane, I compared the spatiotemporal dynamics of forage resources between each area across the summer. I developed dynamic foodscapes representing forage metrics using data from field-estimates of forage quality and quantity and in situ captive-caribou foraging trials. Results supported my hypothesis that caribou in Cochrane were in a lower-nutritional plane than Pickle Lake, largely because accepted biomass and intake rates averaged higher in Pickle Lake than Cochrane and high-quality accepted biomass peaked ~1 month later in Cochrane indicating a possible trophic mismatch. I used the dynamic foodscapes in conjunction with spatial maps of wolf predation risk to understand if caribou of different reproductive states (barren, calf lost within 5-weeks postpartum, and calf survived at least 5-weeks postpartum) traded off their foraging opportunities under high predation risk to further understand foraging dynamics of caribou in these environments. I found that caribou selection was most closely tied to intake rates across calving to late summer irrespective of reproductive state, but caribou traded off higher intake rates for safety at areas of high predation risk. Caribou that made the least forage-predation risk trade-offs during calving lost their calf. Compared to other reproductive states, caribou whose calf survived at least 5-weeks postpartum selected for higher intake rates before making trade-offs for lower predation risk during early and late summer, which was after the energetically demanding period of peak lactation.
    Results of my thesis suggest that caribou adjust their calving behaviors across a gradient of available conditions. Given caribou selection for mid-late seral (>20 years) upland and lowland conifer forests void of linear features, and the effect it can have on expressing habitat fidelity, management may enhance calving opportunities for caribou by protecting these forest characteristics. Given the role neonatal recruitment can have on population dynamics of caribou, management should prioritize the landscape conditions selected by parturient caribou. Early and late summer may reflect a sensitive period for caribou with a calf-at-heel because they selected for areas of higher intake rates than other reproductive states, which may expose them to higher predation risk. For caribou in northern Ontario predation risk appears to have a strong impact of resource selection and therefore management strategies that minimize risk of predation are critical to their long-term persistence.

  • Subjects / Keywords
  • Graduation date
    Fall 2023
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.