What is the issue?
An estimated 900,000 to 14 million migratory birds are electrocuted annually on electric distribution lines in the U.S.
Why does this happen?
Most electrocutions occur on distribution lines and poles compared to transmission lines. Distribution line conductors are placed closer together than on transmission lines, increasing risk of electrocution on distribution lines. Birds can be electrocuted on transmission lines; however, it is rare and there is a lack of data to evaluate the scale of this problem.
Risk of electrocution occurs when a bird simultaneously touches two energized parts or an energized part and a grounded conductor or equipment. A bird may touch energized parts when flying on or off a distribution pole, when defecating from the pole and causes a connection, or when a large number of birds roost on the lines at the same time, causing them to sway and make connections. The risk of bird electrocutions on a distribution pole is based on the combination of three factors: biological, environmental, and engineering.
A bird’s vulnerability to an electrocution is based on the following characteristics:
- Body size. Large birds are most at risk of touching two parts simultaneously as their wingspan and head-to-foot height is typically greater than the separation between energized components. However, small birds are also electrocuted as they can access smaller spaces where energized components are more closely aligned.
- Age. Young birds are less agile and may be less able to avoid wires and equipment thus increasing risk of electrocution. In addition, juvenile birds are less experienced with hazards on the landscape and require time to adapt to these risks.
- Use of Perches. Many birds, particularly raptors, seek out tall perches to hunt for food and some birds perch and roost on distribution poles. Frequent use of poles increases the exposure to energized parts while flying on and off a pole. Both large and small birds have been observed nesting on distribution poles. Nesting material may cause an electrical connection, or the nest material could catch on fire, killing the bird and damaging the power structure. Birds that roost on distribution lines in large flocks (e.g., swallows) can cause lines to sway and touch.
In addition to biological factors, other environmental factors influence electrocution risk:
- Habitat Type. Studies indicate that electrocutions are more likely to happen in habitats with low vegetation where the distribution pole is the (or one of the) tallest structures in the habitat. Given a bird’s preference for elevated perches for protection from predators or to obtain a higher vantage point for hunting, distribution poles that are prominent features on the landscape will likely have greater use than poles in landscapes with other tall structures or trees. Urban or disturbed areas are generally characterized as low quality habitats.
- Wet Weather. In dry conditions, feathers are not good conductors of electricity. Electrocution typically requires skin or bone contact (e.g., wrist to wrist) with the energized parts. However, when feathers are wet, they have a higher conductivity and electrocutions occur with wingtip to wingtip connections.
- Seasonal Variation. Birds are electrocuted year-round and studies vary on whether one season is of greater risk than others. During breeding season, more birds may attempt to nest on distribution poles, while in the fall there are more juveniles on the landscape, and finally in winter, some species congregate in large numbers, potentially increasing risk of pole use.
The critical factor that increases the risk of bird electrocutions on distribution poles is the distance between energized parts. This distance can be between components horizontally (where a bird typically connects the circuit with its wings) or vertically where a bird might make a connection with its body (head to foot distance). Ultimately, the design of a pole influences risk through:
- Phase design. The number of phases and phase separation distance directly influences electrocution risk.
- Pole type. Metal poles commonly used in Europe and increasingly used in the U.S. are higher risk for electrocutions than other materials.
- Pole equipment. Transformers, jumper wires, surge arresters, switch equipment, etc. increase the number of energized parts that can make connections when touched.
Mortality studies indicate that a large number of birds experience electrocutions on distribution poles. While some affected birds types may be undercounted and specific types of birds may be affected more in some areas than others depending on pole locations (e.g., increased risk of waterbirds near water), many types of birds can be electrocuted. Bird types most commonly electrocuted include:
- Raptors. Eagles and buteos are of primary concern due to their large size, preference for nesting, roosting, and hunting from tall perches, especially in open habitats.
- Waterbirds. Herons and storks may use poles near wetlands to roost, dry feathers, and nest. This taxa may have increased risk due to large size and frequency of having wet feathers
- Vultures and Condors. Very large birds that are known to roost on power poles
- Corvids. Species of raven and crow frequently nest and roost on power poles and are of medium size that can make the connection between energized parts on many poles.
- Songbirds. Smaller birds such as shrikes and kingbirds commonly try to nest on poles in small spaces created by pole equipment and wires.
What are some solutions?
In the U.S., bird impacts from electric utility infrastructure gained national attention in the 1970s. In 1989, conservation agencies and electric utility companies formed the Avian Power Line Interaction Committee (APLIC) to understand the hazard and reduce bird impacts.
Solutions to this issue protect not only birds, but also power supply reliability, as electrocutions can cause power outages, damage equipment, and increase costs of operation and maintenance of the supply system.
APLIC has taken great strides in engaging electric utility companies nationwide, and developing resources and information critical for addressing electric utility line impacts to birds. There are now proven solutions to bird electrocutions on distribution poles, whereas the science of power line collisions continues to have great uncertainty.
Avian electrocutions on distribution poles are preventable with little expense to the operator with the right pole design and/or use of insulation materials. The most cost-effective approach to reduce bird electrocutions is to focus retro-fitting efforts on poles and in areas with the highest risk to birds. Electrocution risk is reduced when the distance between energized parts and grounded parts is increased or some of the parts are insulated to create separation.
Specific APLIC recommendations for reducing electrocution risk to birds are as follows:
Pole Design – Distribution poles are considered avian safe if they meet the following conditions:
- The horizontal separation between all energized parts and between energized parts and grounded equipment is at least 60 inches.
- The vertical separation between all energized parts and between energized parts and grounded equipment is at least 40 inches.
- Phases or grounds where adequate separation is not feasible are covered. Examples of covers include insulator/conductor covers, bushing covers, arrester covers, cutout covers, and jumper wire covers. Cover designs should be evaluated and approved by company engineers prior to use.
Benefits of fixing pole design:
For more detailed information on causes and solutions for avian electrocutions on power lines, visit the APLIC website, the Electrocutions webpage and Suggested Practices for Avian Protection on Power Lines.
To read more about the causes and solutions for electric utility lines and bird collisions, see the Electric Utility Lines page.
Material on this webpage was sourced from: APLIC 2006, Demerdzhiev 2014, Dwyer et al. 2014, EDM 2014, Janss and Ferrer 2001, Kershner et al. 2004, Lehman 2001, Lehman et al. 2007, Loss et al. 2014, and Manville 2005.