NESTING BY RAPTORS AND COMMON RAVENS ON ELECTRICAL TRANSMISSION-LINE TOWERS

Raptors and common ravens (Corvus corax) (hereafter called ravens) beg an nesting on towers along a 596-km segment of a 500-kV transmission l ine in southern Idaho and Oregon within 1 year of its construction. We began monitoring these nesting populations in 1981 to assess the effe ctiveness of artificial structures in attracting nesting raptors and t o provide guidelines for enhancing raptor nesting opportunities on tra nsmission lines. Within 10 years, 133 pairs of raptors and ravens were nesting along the 500-kV line. Rapid colonization of towers along the line probably was due to lack of other nesting substrate in the trans mission line corridor, and the proximity of existing nesting populatio ns in the nearby Snake River Canyon. Transmission towers provided both new and alternative nesting substrates. Raptors and ravens used all t ypes of towers on the line but preferred (all P < 0.05) tower types an d sections of towers where steel latticework was relatively dense. The y tended to nest on the same or adjacent towers each year even though a low percentage of nests remained intact after the breeding season. D estruction of nests by wind was the most common cause of nest failure on transmission towers. Artificial platforms protected nests from wind damage, and hawks and eagles showed a preference for platforms. Overa ll nesting success of pairs on transmission towers was similar to or h igher than that of pairs nesting on other substrates. Utility companie s can enhance raptor nesting opportunities and minimize conflicts with power transmission by providing stable nesting substrate that is not directly above insulators. Nest site modifications either during or af ter line construction can attract nesting raptors and improve their ne sting success.