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.