Raptors and Power Lines
There are many species of Raptors that inhabit various locations throughout the world. Typically, Raptors consist of Hawks, Falcons, Kites, Eagles, Vultures and Owls and are collectively known as “birds of prey”. Iconic birds such as the Bald Eagle, previously close to extinction, have made a dramatic turn around in numbers in recent times due to various initiatives and measures to protect the species.
Despite the above efforts, some of these species continue to be threatened and are in alarmingly low numbers. One ongoing threat to Raptors and their population numbers are Power Lines. Raptors due to their size and foraging habits, can fall victim to Power Lines (both Distribution and Transmission) for a number of reasons.
Two primary reasons are collisions and electrocutions.
More likely to occur on Utility Distribution poles and wires due to their proximity or closer clearances. Typically, Raptors can perch on the Cross Arm of the Pole and this unfortunately can bring them into close contact with the live electricity. Typical Utility assets include 3 phases, one per wire.
These phases can be at different spacings and voltage, but many Raptors have wing spans which can easily eclipse this spacing. If this occurs, then the bird effectively creates a “bridge” between these phases which can lead to injury or death of the bird. Because Raptors typically do not reside or inhabit urbanised areas, the power lines are often medium voltage distribution assets (typically 11KV to 33KV) in rural or less populated areas. Unfortunately at these voltages, the Raptors are extremely vulnerable.
Collisions can occur on both Utility Distribution poles and wires as well as Transmission lines. Due to the elevated height of Transmission lines, they are often at an altitude which coincides with birds flight patterns or migratory habits. It is known that the Ground or Earth wire on these Transmission lines are particularly problematic to birds. This is theorised because the birds may see the thicker and more obvious phase wires which are typically lower down. Once they see the phase wires, they may execute an avoidance flight path by pushing higher. This unfortunately can bring them into direct contact with the much thinner and harder to see Ground wire.
Raptors, because of their somewhat unique foraging behaviour, can focus their attention on the ground. From an evolutionary standpoint, Transmission towers are still a relatively new phenomenon, and it may be that Raptors and other bird species, are yet to evolve or adapt to this artefact in their landscape. With this theory in mind, it is reasonable to expect that this is a contributing factor to potential collisions between Raptors and Power lines. This also explains why Raptors may be vulnerable to this despite their excellent acuity of vision. Let’s proceed to the strategies that can be adopted for raptor protection on powerlines.
One well known and effective mitigation strategy to prevent power line collisions is the deployment of Bird Diverters. These Diverters or Flappers, are typically moveable devices with contrasting colours and other features which create a visual warning for the birds of an impending structure.
They effectively make the Power Line onto which they are installed much more visible than it otherwise would be.
There are two main types of Bird Diverters
- Flappers, which are typically devices which attach and hang under the Power Line and employ movement as their main visual stimulant.
- Static Diverters, these are typically spiral in shape and wrap around the Power Line. They have the advantage of being cost effective (though can be more labour intensive to deploy) and stable from a durability standpoint.
The main advantage of type 1 Bird Flappers, is how effective the element of movement is at capturing the attention of any species which is highly dependent on its visual centres. Birds are no exception and any device which agitates with wind creates a constantly moving stimulus which has a much greater visual impact.
The statistics reveal the magnitude of the problem:
At the US Fish and Wildlife Service’s National Forensics Laboratory, from 2000 to 2015, 417 raptor deaths were determined to have been caused by electrocution. … Today, power lines are still a significant cause of death, fatally electrocuting an estimated 0.9 to 11.6 million birds each year.
In a world where electricity is becoming increasingly vital to a modern way of life. Electricity assets will continue to provide a potential danger point for wildlife. Utilities and Engineers understand this and routinely take proactive steps to mitigate these problems. Bird diverters are one such way to minimise the impact of bird fatalities and injuries due to collisions with Power Lines.