Calving behavior of boreal caribou in a multi-predator, multi-use landscape

  • Author / Creator
    DeMars, Craig A
  • The boreal ecotype of woodland caribou (Rangifer tarandus caribou) is federally listed as Threatened due to population declines throughout its distribution. High mortality rates of neonate calves (≤ 4 weeks old) due to predation are a key demographic factor contributing to population declines and increasing predation has been linked to landscape disturbance within and adjacent to caribou range. To inform management strategies for improving rates of calf survival, I investigated the space use and habitat requirements of female boreal caribou during calving. Space is integral to the calving behaviour of boreal caribou with parturient females dispersing widely on the landscape, a behaviour hypothesized to reduce predation risk. I assessed potential evolutionary drivers of dispersion using simulation analyses that tracked caribou-wolf encounters during the calving season. I specifically assessed whether dispersion decreased predation risk by: (i) increasing predator search time, (ii) reducing predator encounters because individuals are inconspicuous relative to groups, or (iii) eliminating the risk of multiple kills per predator encounter of caribou groups. Simulation outputs show that dispersion only becomes favourable when differential detectability based on group size is combined with the risk of multiple kills per encounter. This latter effect, however, is likely the primary mechanism driving parturient females to disperse because group detectability effects are presumably constant year round. Simulation outputs further demonstrate that if females become increasingly clumped – a pattern that may result if caribou avoid disturbance in highly impacted landscapes – then calf survival is negatively affected. To specifically identify key attributes of calving habitat, I used a three-step process. First, I identified GPS locations where females were accompanied by neonate calves by developing two novel methods for predicting parturition events and neonate survival status based on female movement patterns. These methods predicted parturition with near certainty and provided reasonable estimates of neonate survival, which I further augmented with aerial survey data. Using the partitioned GPS location data, I then developed resource selection functions using a generalized mixed effects modelling approach that explicitly maintained the individual as the sampling and comparative unit. I discriminated calving areas from other areas within caribou range by conducting multiple comparisons based on season and maternal status. These comparisons show that parturient females shifted from bog-dominated winter ranges to calving areas dominated by fens. In general, reducing predation risk was a dominant factor driving calving habitat selection although the shift to fen landscapes indicates that females may be trading off increased predation risk to access higher quality forage because fens are riskier than bogs. As a third step, I explicitly evaluated calving habitat quality by relating maternal selection and use of resources to the probability of neonate survival. These analyses included spatially explicit covariates of predator-specific risk. Surprisingly, variation in landscape disturbance had minimal effect on calf survival; rather, survival was best explained by predation risk from black bears (Ursus americanus). Collectively, my findings yield important insights into the habitat requirements of boreal caribou during calving and highlight that management actions aimed at improving calving habitat quality will need to be conducted at large spatial scales.

  • Subjects / Keywords
  • Graduation date
  • 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.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
    • Department of Biological Sciences
  • Specialization
    • Ecology
  • Supervisor / co-supervisor and their department(s)
    • Boutin, Stan (Biological Sciences)
  • Examining committee members and their departments
    • Merrill, Evelyn (Biological Sciences)
    • Derocher, Andrew (Biological Sciences)
    • Kauffman, Matthew (University of Wyoming, Dept. of Zoology and Physiology)
    • Nielsen, Scott (Renewable Resources)