Let there be lights, to help migratory cranes avoid power lines

Cranes are celebrated for their large size, beauty, unique courtship dancing, and extensive annual migrations.

Sandhill cranes (Antigone canadensis), for example, migrate north each year from wintering grounds in Mexico and the southwestern United States to breeding sites across Canada, the northern U.S., and eastern Siberia. Along the way, they stop to rest and refuel at various wetlands and river basins of the western and midwestern U.S.

Stopover points are essential to the birds’ migrations and subsequent breeding periods. Although the loss of wetland habitats at stopover and breeding sites is the main threat to sandhills and other cranes, midflight collisions with power lines during migration affect 12 of the world’s 15 crane species, including sandhills.

Electric utility companies mark power lines with glow-in-the-dark line markers to try to mitigate the problem. These attempts to make power lines more visible to these large birds have been only partially successful, however, as most collisions occur at night, when the power lines are least visible to birds.

A new approach considers bird vision

A team of engineering consultants at EDM International has developed a new system that shines near-ultraviolet (UV) lights on power lines, as many bird species are sensitive to UV frequencies. The team tested its system, which it calls the Avian Collision Avoidance System, or ACAS, at a major migratory stopover site for many thousands of sandhill cranes.

Hundreds of sandhill cranes die each year by colliding with the power lines at their testing site, the Iain Nicholson Audubon Center at Rowe Sanctuary in Nebraska’s Central Platte River Valley, despite the lines having previously been marked with line markers.

Use of the new system substantially reduced the number of collisions between the cranes and a power line that crosses the Central Platte River. The team published its findings and system designs earlier this year with the hopes of advancing a solution to the conflict between human structures and migratory wildlife.

In searching for a better way to reduce bird-power line collisions, lead author James Dwyer and colleagues learned that many groups of birds are sensitive to energy wavelengths shorter than what humans can detect, which is roughly 400 nanometers (nm). They developed the ACAS using near-ultraviolet wavelengths of 320 to 400 nm to make the power lines more visible to the cranes without increasing their visibility to people.

The system design mounts the UV lights on the supporting structures of a problematic power line and shines the lights on the line itself.

“The lights go on the existing tower that holds up the power line,” Dwyer told Mongabay. “Ideally they go on the crossarm or lattice arm that supports the wires.”

The construction they tested consisted of four low-wattage UV-A lights, powered by two solar panels and storage batteries, a control box, cables connecting the various components, and a remote control. The authors estimated their total cost came to roughly $6,000, including some UV lights they tested but didn’t deploy in their final version.

They tested the ACAS between February and June of 2018, the period when migrating sandhill cranes were in the area. The team randomly assigned the system to be on or off each night, and, from a blind, they watched the behavior of flocks of cranes flying along the river for about five hours on test nights, from dusk to four and a half hours after sunset.

They recorded any collisions with the approximately 15-meter-high (50-foot) power line, the birds’ flight behavior after a collision, and their reactions as they approached the power line. The observers also estimated the perpendicular distances with which cranes flying up the river reacted to the power line, with reactions within 25 meters (80 feet) of the line considered risky or dangerous.

The observers considered reactions that resulted in the cranes passing over the power line at heights less than 25 meters as “dangerous” flights, even if no collision occurred.

A surprisingly strong result

During the four-month study, they recorded 916 flocks of cranes passing the power lines and 49 collisions, only one of which occurred when the ACAS system was on. In addition to this 98 percent reduction in collisions, they also documented 82 percent fewer dangerous flights and quicker, more controlled reactions by the cranes to avoid hitting the power lines when the system was on.

“We think the birds could clearly see the line in the dark even though it was still invisible to us,” Dwyer said.

In a statement, Dwyer said he was surprised at the strength of the findings. “I thought perhaps there could be a more effective approach” to reducing collisions, he said. “I thought it would have some effect, but I didn’t dare think the ACAS would pretty much solve the sandhill crane collision problem at our study site on our first try.”

The ACAS developers want to expand their project to other locations and species. “Installation and monitoring is 100% replicable,” Dwyer said. “We need to do more studies with other species, habitats, line configurations, etc., to see if the results are replicable.

“We are very interested in collaborating at other sites to conduct additional testing,” he added.

The authors suggest in their paper that UV lights could also help to reduce collisions of large migratory birds with wind turbines, as well as keep smaller migrants far from buildings, towers, and other structures that become deadly at night. As power lines and wind turbines proliferate, the authors propose testing various configurations of lights to illuminate the most problematic parts of structures and to be sure the lights don’t affect behavior of insects or other wildlife.

Citation:

Dwyer, J. F., Pandey, A. K., McHale, L. A., & Harness, R. E. (2019). Near-ultraviolet light reduced sandhill crane collisions with a power line by 98%. The Condor: Ornithological Applications, 121(2). doi:10.1093/condor/duz008

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