Why do birds hit electricity lines?

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In order to meet U.S electricity demands, thousands of miles of distribution and transmission lines crisscross the country.  Typically, electricity delivery includes power generation at a power plant or a renewable energy source that is moved to transfer substations by transmission lines.  Once at the substation, electricity is transferred to distribution lines that carry the power to the end user (i.e., homes and businesses).

Distribution poles are the most numerous component of the electrical system, and are spaced approximately 200 feet apart for an average of 26 poles/mile of line.  There are an estimated 116 million to 185 million distribution poles in the U.S.

It is currently estimated that between 8 million and 57 million birds are killed in the United States annually from collisions with electric utility lines.  Combined with bird impacts from electrocutions, bird mortalities resulting from electric utility lines have been a long-standing bird conservation issue. Electric utility infrastructure continues to increase; resolving conflicts between birds and power lines continues to be an important focus of bird conservation efforts both in the U.S. and around the globe.

Why does this happen?
Electric lines are obstructions typically placed within the range of average bird flight level and are difficult for birds to see. Birds can be injured or killed with they collide with electric lines in mid-flight. Electric lines are a particular risk in locations frequently traveled by birds and in areas where poor weather or darkness could further decrease visibility.

Although birds of all sizes and types collide with wires, their behavior and body type put them more at risk for line collisions.  For instance, herons, egrets, raptors, and storks breed and roost in elevated areas such as trees and poles, which makes their daily exposure to these areas much higher than other ground roosting and nesting birds.  In addition, herons, egrets, and storks, as well as many species of waterfowl and cranes, travel between breeding, feeding, and roosting sites in flocks.

All these behaviors increase the possibility of a bird’s exposure to electric lines.  In fact, it was an incident involving collisions of Whooping Cranes with transmission lines in the1980s that spurred important advances in the work being done to reduce bird collisions with electric utility lines.

What are some solutions?
In the U.S., the issue of bird impacts from electric utility infrastructure, resulting from both collisions and electrocutions, gained national attention in the 1970s. Consequently, conservation agencies and electric utility companies formed the  Avian Power Line Interaction Committee (APLIC) to understand the hazard and reduce the number of annual bird impacts.  Solutions to this issue not only protect birds but also protect power supply reliability as electrocutions can cause power outages, damage equipment, and increase costs of operation and maintenance of the supply system.

To date, there are proven solutions to bird electrocutions on distribution poles, whereas the science of power line collisions continues to have great uncertainty.  Because of this uncertainty, prevention mechanisms for reducing bird collisions with line infrastructure are not yet as well established and confirmed in effectiveness as they are for electrocutions.

Even though more research is needed in this area, a number of options are currently recommended and available in APLIC’s document  Reducing Avian Collisions with Power Lines: State of the Art in 2012, including the following:

  • Marking lines;
  • Managing surrounding lands;
  • Removing shield (i.e., ground) wires;
  • Changing the size or configuration of wires;
  • Rerouting the line; and
  • Burying lines when practical.

For more information about measures and guidance for avoiding and minimizing impacts to migratory birds from electric utility lines and other sources, please visit the Conservation Measures and Guidance Documents webpages.

– From U.S. Fish & Wildlife Service

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