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


Other title
animal movement
black bear
boreal caribou
space use
habitat quality
Rangifer tarandus caribou
habitat selection
Type of item
Degree grantor
University of Alberta
Author or creator
DeMars, Craig A
Supervisor and department
Boutin, Stan (Biological Sciences)
Examining committee member and department
Nielsen, Scott (Renewable Resources)
Kauffman, Matthew (University of Wyoming, Dept. of Zoology and Physiology)
Derocher, Andrew (Biological Sciences)
Merrill, Evelyn (Biological Sciences)
Department of Biological Sciences
Date accepted
Graduation date
Doctor of Philosophy
Degree level
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.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
DeMars, C.A., Auger-Méthé, M., Schlägel, U.E. & Boutin, S. (2013). Inferring parturition and neonate survival from movement patterns of female ungulates: a case study using woodland caribou. Ecology and Evolution, 3, 4149–4160.

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