2009

Collisions with powerlines cause substantial mortality among many species of birds, but such losses may be reduced by installing devices that make powerline wires conspicuous. During 5 March-18 April 2008 and 3 March-13 April 2009, we investigated mortality of sandhill cranes (Grus canadensis) stemming from collisions with two 69-kilovolt (kV) powerline arrays at a major night roost of the species on the Platte River in Buffalo County, south central Nebraska. Static wires of each powerline were equipped with FireFly™ bird diverters (FireFly Diverters LLC, Grantsville, Utah).

We searched for carcasses of cranes at sandbars, islands, and shallow water areas between riverbanks below each powerline three times weekly and attempted to account for detectability biases. An estimated 50-93 sandhill cranes were killed by the two powerlines in 2008 and 37-70 were killed in 2009. These estimates were one-half to one third of that reported in a previous study at the site, before FireFlys were installed.

Using binoculars and night-vision scopes, we observed 101 and 117 collisions by sandhill cranes at one of the powerlines in 2008 and 2009, as the cranes returned to their roost from about 0.5 hours before sunset until about 2 hours after sunset. Most collisions occurred when flocks of more than 1000 cranes suddenly flushed from their roost within 0.5 km of the powerline after dusk. There appeared to be no relationship between collision incidence and weather or light conditions. About one-half of cranes that collided fell immediately to the ground, either dead or crippled. Another 29% continued to fly after striking wires, but their flight was hampered. About 65% of observed collisions involved static wires. We also observed reactions of 474 flocks of sandhill cranes to the powerline in 2009. Cranes reacted more quickly to avoid the powerline than they did to powerlines not equipped with diverters or to powerlines equipped with 30-cm yellow aviation balls as diverters in a previous study in south central Nebraska, and did so mainly by gradually climbing in flight.

Individual wires on the powerline we observed also were instrumented in 2009 with bird strike indicators (BSIs), a new electronic technology to detect bird collisions. Collision incidents we observed and those indicated by BSIs were highly correlated. Diel records from BSIs indicated one-half of collisions by birds occurred during evening; nearly all the rest were distributed across remaining night hours. Our results might suggest FireFlys reduce the likelihood that a sandhill crane will collide with powerlines at Rowe, but more rigorous experimental design incorporating replication is needed to reliably assess and provide broader inferences on effectiveness of FireFlys in decreasing mortality of cranes and other bird species at powerlines. BSIs should be further evaluated and incorporated into such assessments.