Avian Conservation and Ecology (Jun 2022)

Mortality of grassland birds increases with transmission lines

  • Caroline J. Martin,
  • Edward W. Bork,
  • Scott E. Nielsen

Journal volume & issue
Vol. 17, no. 1
p. 17

Abstract

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Electrical transmission line development has been expanding globally by 5% per year, leading to increases in avian collisions with lines. Canadian estimates of transmission line collision mortalities range from 2.5 to 25.6 million birds per year, with the majority of mortalities attributed to collisions with overhead shield wires, and by susceptible birds that are young, large-bodied, with low maneuverability, or in open habitats. In this study, avian mortality was estimated for a ~4900 ha area in the mixed-grass prairie of southeastern Alberta following construction of two major transmission lines. We surveyed seven 500 m transects 7–10 times during both the breeding and migration seasons, where transects were categorized into road (n = 2), transmission line (n = 2), wetland (with transmission lines above; n = 1), or control (n = 2) areas. During the 2016 breeding season (5 May–24 June), we detected 23 mortalities under transmission lines, 7 mortalities beside roads, and no mortalities in controls. In the 2017 spring migration season (31 March–5 May), we detected 24 mortalities under transmission lines, 3 mortalities beside roads, and no mortalities in controls. Mortality rates were adjusted with biases estimated from detectability and scavenging trials. Scavenging rates were high (82% of carcasses were scavenged within 5 days) and detectability of deceased birds was positively related to body size. Overall, linear disturbances within the study area, including 37.7 km of highways and transmission lines, contributed to an estimated 75 deaths/km of linear disturbance during one migration and one breeding season (~50 deaths/km of transmission line and ~25 deaths/km of road; ~1904 bird mortalities total). These findings point to the need for mitigation to reduce bird mortality, thereby minimizing the long-term impact of linear disturbances, such as transmission lines and roads, on associated bird communities.

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