Perch management has historically been used by the electric industry to keep raptors from perching on certain parts of structures that may pose an electrocution risk to birds of prey. In recent times, perch management has been a required mitigation measure for new transmission lines that occur in habitat of the Greater and Gunnison Sage-Grouse (Centrocercus urophasianus and C. minimus, respectively) on lands managed by the Bureau of Land Management and the US Forest Service in an effort to limit the frequency and duration of raptors' perching on transmission and distribution structures including pole tops. In central Wyoming, Tri-State Generation and Transmission Association, Inc. (Tri-State) installed perch deterrents comprising spiked pole caps on pole tops and nest diverters over conductor fittings to manage potential perching and nesting by raptors. An unknown percentage of 59 pole caps were field-modified during installation to fit smaller or larger pole-top diameters than recommended by the manufacturer. The modifications were applied without consulting the biological team that specified and purchased the equipment, or reporting the modifications thereafter. Over 3 yr post-installation, we documented failure of the spikes on the pole caps at an average rate of 0.92 spikes lost per month. Nest diverters (n = 66) installed on these same structures were not modified and did not fail, though nest diverters lacked a protruding spike so were perhaps less prone to failure. Our findings are novel in quantifying potential negative effects to perch-management equipment that is field-modified during installation. This is informative because degradation of perch-management equipment designed to reduce electrocution risk to raptors or reduce raptor predation on prey species of conservation concern may undermine conservation goals. Resource managers working to minimize the environmental impacts of power lines can use this information to better anticipate concerns in power pole retrofitting that may derive from field-modification of retrofitting equipment.
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Vol. 54 • No. 2