Testing nest deterrents for Chihuahuan ravens on H-frame transmission structures

Chihuahuan ravens (Corvus cryptoleucus) regularly perch and nest on electric utility structures. Because ravens perch on overhead shield wires, for which no perch discourager exists, management focuses on nests. When nests occur above energized wires (phase wires), risk of line faults, pole fires, and power outages develop. In southeastern Colorado, USA, Chihuahuan ravens nesting on H-frame transmission structures historically nested exclusively above the center phase. Nest deterrents prevent ravens from nesting over the center phase on short line segments (1.5 km), but effectiveness over longer line segments is unknown. We installed nest deterrents over the center phase on all structures within a 25.7-km line segment (n= 93 structures), and compared nesting there with nesting on two 0.75-km untreated segments adjacent to each end of the treated segment (n= 10 adjacent structures) and on a 25.6-km untreated segment (n= 93 distant structures). Data were collected over 7 surveys in Bent, Kiowa, and Crowley counties in southeastern Colorado, spring 2012. Ravens placed nest material on 25.8% of treated structures, 90.0% of adjacent untreated structures, and 78.5% of distant untreated structures. Used nests (containing eggs or nestlings) occurred on 2.1% of treated structures, 40.0% of adjacent untreated structures, and 17.2% of distant untreated structures. No used nest occurred above the center phase on any treated tangent structure, whereas all used nests occurred above the center phase on untreated structures. Future research should evaluate whether placing deterrents above all phases further reduces nesting. If so, this application could also be used in areas where ravens are potential predators of species of special concern.