Displacement and Mortality of Birds by High Voltage Transmission Lines in the Canadian Dry Mixed Prairie

  • Author / Creator
    Martin, Caroline
  • Canadian grasslands are continuing to experience loss in habitat and degradation in quality due to agricultural expansion and fragmentation from roads, pipelines, and transmission lines. Today, only 43% of Canadian mixed grass prairie remains. This loss and fragmentation has led to a decline in grassland songbirds, with further reductions predicted as urban-industrial expansion continues. The construction of new high-voltage (>500 kV) transmission lines through the Mattheis Ranch in Southeastern Alberta in 2014-15 provided a unique opportunity to examine the effects of transmission line construction on grassland songbird occupancy and mortality. Baseline data collected at 168 sites across a 3,500 ha area from before transmission line construction in 2012–13 was compared to data collected after construction in 2016, as well as on control sites located >1500 m from transmission lines. The same 168 sites were sampled 3 times during the pre- and post-construction sampling periods, for a total of 6 sample periods, in the breeding seasons (May-June) of 2012-13 and 2016. Plots were run in transects and further blocked into treatments: transmission line only, highway only, highway and transmission lines on one side (one-sided), highway and transmission lines on both sides (split), and controls. Species richness did not differ between years, but a greater number of species was found in treatments with highways present. Corvids were more common near transmission lines after construction, while perching birds like the western meadowlark and Sprague’s pipit were more common further from transmission lines after construction. Six focal species – Baird’s sparrow, Brewer’s blackbird, Eastern kingbird, grasshopper sparrow, long-billed curlew, and marbled godwit – that represented a variety of functional groups, had different responses to powerline construction. The Brewer’s blackbird was negatively affected by transmission lines, while the Baird’s sparrow, Eastern kingbird, grasshopper sparrow, and long-billed curlew were positively affected. Marbled godwits showed no response. Mortality due to collisions with transmission lines may also be contributing to declines in grassland birds, with estimates of between 2.5 to 25.6 million birds killed by transmission line collisions per year across 231,966 km of lines in Canada. There are over 3,800 km of transmission lines in the Canadian mixed-grass prairie. This study estimated avian mortality due to collisions with powerlines in a mixed-grass prairie. In the breeding season (May-June) of 2016 and the migration season (March-April) of 2017, two observers searched for bird carcasses along seven 500-m transects on the Mattheis Ranch with two transects beside highways, three under transmission lines, and two in controls where neither disturbance was present. Detectability and scavenging trials were conducted in 2016 to estimate bias in mortality estimates based on detectability (sightability and loss from scavengers). During the breeding season of 2016, 23 mortalities were recorded under transmission lines, 7 mortalities were found near roads, and no mortalities were found in controls. Subsequently, 24 mortalities were found under transmission lines in the spring migration season of 2017, 3 mortalities were found near roads, and no mortalities were found in controls. Scavenging rates were greater in this study (82% of carcasses were scavenged within 5 days) than reported in non-grassland habitats. Overall, linear disturbances within the immediate study area (Mattheis Ranch), including highways and high-voltage transmission lines, have the potential to contribute to the loss of 1,948 to 1,970 birds during one migration and breeding season (3,918 over a spring season). When considering all transmission lines in the Canadian mixed-grass prairie of Canada, I estimated a loss during the spring migration and breeding season of 192,316 birds. These findings point to the need for greater mitigation actions to prevent future losses of birds in areas where linear disturbances occur. Changes in vegetation, predator presence, and transmission lines functioning as ecological traps may be contributing to these changes.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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