The Implications of Animal Movement on Camera Detections as a Means to Monitor Density

  • Author / Creator
    Broadley, Kate R
  • Camera traps are an increasingly popular tool for wildlife management. Studies that use detection rates as a simple index of relative abundance assume that movement is not density-dependent. More complex techniques such as spatially-explicit capture recapture models, occupancy models, or N-mixture models make various assumptions about animal home range size in relation to camera spacing. While some assume individual animals can visit multiple camera sites, others assume sites are independent such that no individual can be detected at more than one camera. In all these methods, variation in space use has the potential to confound population estimates and compromise current applications of camera trapping as a monitoring tool. To assess this problem, I quantified how movement rate and home range size vary both between and within populations, and investigated the implications of this variation for camera trap data analysis. To quantify the relationship between space use and population density, I conducted a meta-analysis of studies reporting movement rate, home range size, or density for at least two populations of terrestrial mammals. I found that movement rate and home range size are significantly negatively correlated with density and positively correlated with each other. Using simulations of animal movement and density, I found that density-dependent movement can obscure trends in density indexed by detection rates. True changes in density may be underestimated by up to 30%. I then investigated space use within populations using telemetry datasets for white-tailed deer, moose, and wolves. Patterns between individuals were similar to those patterns seen between populations, where individuals with larger home range sizes generally had faster movement rates. Variation between individuals within a population was an order of magnitude greater than variation between the mean movement rates and home range sizes of different populations. Carnivores in particular exhibited much greater variation between individuals than herbivores. These findings indicate that choosing camera spacing appropriate for a given model is not straightforward, as some individuals are likely violating the model assumptions regarding site independence. I recommend that practitioners treat camera trap detection rate indices of relative abundance as good indicators of directional population trends and as partially accurate indicators of the actual magnitude of density changes. Furthermore, I urge that practitioners be aware that individual variation in space use is considerable, and that assumptions regarding camera spacing relative to animal home range size are likely often violated. Animal space use is an important subject for the ongoing development of robust camera trap analyses, and I hope that this thesis will encourage a more careful consideration of its role in the design of future camera trapping studies.

  • Subjects / Keywords
  • Graduation date
    Fall 2017
  • Type of Item
  • Degree
    Master of Science
  • 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
  • Specialization
    • Ecology
  • Supervisor / co-supervisor and their department(s)
  • Examining committee members and their departments
    • Mathot, Kimberly (Biological Sciences)
    • Bayne, Erin (Biological Sciences)
    • Burton, Cole (Biological Sciences)