Abstract
AbstractThe quantification of bird mortality due to collision with power lines is complicated by the heterogeneity of survey methods used and the bias related to searching for carcasses on the ground (e.g., carcass persistence and imperfect detection by observers). To estimate the bias associated with ground search surveys, we conducted three 30‐d trials to test carcass persistence by placing and monitoring carcasses of red‐legged partridges (Alectoris rufa) and common pheasants (Phasianus colchicus) below power lines at 14 sites. We also conducted two detection experiments, testing the ability of 19 observers to detect bird carcasses. We used survival analysis and generalized linear mixed‐effects models to investigate the effects of site, habitat, carcass size, and survey period on both carcass persistence and detection. We also investigated the effect of carcass age on carcass persistence and the effect of the observer on carcass detection. Our findings show significant variations in carcass persistence between sites and survey periods, as well as significant interaction between these variables. The daily carcass persistence probability was highly variable between sites, with an up to eightfold variation. Carcass detection increased with increasing carcass size and was significantly affected by the microhabitat surrounding the carcass; it also varied between observers. These findings suggest that both carcass persistence and detection vary strongly and unpredictably at a small scale. As a result, conservation managers should be encouraged to conduct carcass persistence and detection experiments on sites where they aim to produce unbiased estimates of bird mortality below power lines, and these trials should be carried out in conditions similar to the mortality survey. A large‐scale, unbiased, and accurate estimate of bird collision mortality due to power lines may require substantial field effort, with a survey frequency of more than once a week.
Highlights
In today’s modern societies, most human activities, industrial or domestic, involve the use of electricity
Four aspects can contribute to underestimating this mortality: (1) the removal by scavengers of carcasses under power lines, that is, carcass persistence (Kostecke et al 2001), (2) the difficulty for observers to detect carcasses, that is, carcass detection (Rivera-Milan et al 2004), (3) the accessibility of sites under power lines for effective prospection, that is, habitat bias (Huso and Dalthorp 2014), and (4) the flight of wounded birds that die outside the search area, that is, crippling bias (Bech et al 2012)
We expected to observe highly deterministic scavenger behavior, with scavengers habituated to finding food under power lines and regularly prospecting underneath the linear infrastructure of power lines (Meunier et al 2000)
Summary
In today’s modern societies, most human activities, industrial or domestic, involve the use of electricity. Electricity production choices have required the development of electrical distribution and transmission grids Where these grids have a high density of above-ground power lines, this leads to the death of individuals due to collision with wires (Bevanger 1998, Jenkins et al 2010), species disturbance, and behavioral changes (Deng and Frederick 2001, Shimada 2001, Prinsen et al 2011). Crippling bias is notoriously difficult to estimate experimentally as it requires unbiased monitoring either by direct observation of bird collision with power lines or by telemetry, which is costly in both time and money, as well as ethically sensitive, so this topic has to date been neglected. Only carcass persistence and detection can be estimated experimentally to be taken into account in mortality count estimates
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