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NorthWestern Energy specialists’ paper on bird mitigation to prevent transmission outages published in scientific journal

Jan 29, 2021

Butte, Mont. – Jan. 29 2021 – The first documented sighting of a common raven on the Billings Audubon Christmas Bird Count occurred in 1979. Today populations of the bird have increased significantly in the Treasure State and also across the country. Ravens thrive around humans and the food sources such as landfills that humans create.

Ravens are now a challenge for energy companies because their numbers —flocks of thousands. They roost on power lines and leave droppings on insulators. When the dried droppings combine with fog or light rain, it creates the perfect opportunity for outages.

NorthWestern Energy 500kV Advisor Jim Lueck and NorthWestern Energy Biologist Marco Restani recently published a paper in the scientific journal Human–Wildlife Interactions, a Utah State University Berryman Institute publication. The paper documents the issues with ravens on the 500kV lines and the solutions they found to deal with the birds.

Ravens roost on 500 kV transmission lines near Roundup at dusk. The birds’ droppings can build up on lines and equipment and cause outages when there is fog or light rain. NorthWestern Energy photo

“This was just a clear example of a human wildlife conflict,” Restani said. “Every utility struggles with outages caused by birds through electrocution, collision, nesting, or roosting.”

Publishing the paper was a chance for NorthWestern Energy to share its findings on a common problem that hasn’t been widely studied.

“This was a chance to help other utilities who may also be struggling to identify why they’re having similar type outages,” Lueck said.

It was a stroke of luck that helped solve the mystery of several outages on NorthWestern’s transmission lines.

During the winter of 2016/2017, NorthWestern began experiencing simultaneous outages along the parallel 500kV line segments, our largest capacity transmission lines, running from Colstrip to Washington State.

After each outage, crews patrolled the lines and could not find a root cause. Then late one winter afternoon, Lueck was out with a crew who were working on the 500kV lines. Just as the sun was starting to set, huge flocks of ravens began landing on the 500kV towers to roost for the night.

“It was like something out of a Hitchcock movie,” Lueck said.

After that first chance encounter with the roosting ravens, Lueck started going out in the evenings to investigate. Droppings from the roosting ravens were falling on the insulators. If fog or light rain moistened the droppings, the mixture conducts electricity and creates a bridge along the insulator “skirts,” which causes a fault on the line.

Raven droppings build up on glass insulators that prevent electricity from flowing from transmission lines to the metal support towers. When the droppings get wet from fog or light rain, it conducts electricity and causes an outage. NorthWestern Energy photo

When Restani, who studied ravens for three decades, got involved in the raven/transmission line issue, the huge number of the birds roosting on the 500kV line towers shocked him. One roost alone contained more than 1,500 birds during a single night.

“That’s an astonishing number of ravens,” Restani said.

The paper, titled “The emerging conflict of common ravens roosting on electric power transmission line towers in Montana, USA,” outlines three successful solutions to the problem of raven-caused outages: perch deterrents, periodic washing of insulators and silicon-coated insulators.

The perch deterrents, stainless steel spikes, were installed on portions of the towers. The goal was to prevent or reduce bird droppings from getting on certain insulators.

Power lines are attached to each transmission tower by strings of glass insulators. The insulators keep the electricity from flowing from the line into the metal support towers.

Covering the entire tower in spikes might push the birds to roost on a different structure and would eventually require spikes on a great deal more of the towers. By putting deterrents on part of the known impacted towers, spikes only had to be installed on 92 of the 2,040 towers on the 500 kV transmission lines.

“We actually want to keep the ravens on the towers that they like and manage them there,” Restani said.

Perch deterrents are installed on portions of transmission line towers to prevent or reduce bird droppings from getting on insulators. NorthWestern Energy photo

Insulators still get covered by droppings and need to be cleaned, so NorthWestern Energy uses a helicopter-mounted sprayer. With the helicopter, eight towers can be cleaned in a day compared with one a day by hand. The helicopter can also reach remotes sites on the 500kV transmission line.

Silicon-coated insulators were installed on seven towers with the largest raven roosts as an early proposed solution. These insulators do not need to be cleaned because the properties of the silicon percolate through the droppings, forming discrete droplets so the bird droppings aren’t as conductive, even when wet.

 “NorthWestern is out there ahead of things,” said NorthWestern Energy Director of Environment, Lands, Permits and Compliance Mary Gail Sullivan. “This is pretty cutting edge.”

“We’ve learned so much about this in a very short period of time,” Lueck said. “We have picked up a tremendous amount of information and knowledge in the last three years.”

Lueck and Restani are pleased this paper allows them to share that information with others and hope it helps other energy companies struggling with transmission outage mysteries.

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About NorthWestern Energy (Nasdaq: NWE)
NorthWestern Corporation, doing business as NorthWestern Energy, provides electricity and / or natural gas to approximately 734,800 customers in Montana, South Dakota and Nebraska. We have generated and distributed electricity in South Dakota and distributed natural gas in South Dakota and Nebraska since 1923 and have generated and distributed electricity and distributed natural gas in Montana since 2002. More information on NorthWestern Energy is available on the company's Web site at

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