Many species of birds collide with Power Lines throughout the world every year. Some estimates place the total number of deaths each year in the millions. Some species appear more vulnerable to Power Line Collisions than others.
This is predicted to be due to a combination of factors such as; poor acuity of vision, migration flight paths, flight speed, flight dexterity etc. Species such as Vultures, Bustards, Wildfowl and Cranes amongst others. One particular species in North America, which are particularly vulnerable due to their endangered status are Whooping Cranes. With once over 10,000 Whooping Cranes in North America, these numbers reduced to the brink of extinction.
It was estimated that in the 1940’s there were as few as 15 Whooping Cranes left which formed part of the Aransas Wood Buffalo population. Since measurements were taken, numbers have been gradually climbing due to various proactive measures and last counted around 215 Whooping Cranes. Scientists consider the population must get to at least 1000 Cranes and until this point, their species remains extremely vulnerable to possible extinction. Part of the difficulty in taking proactive measures to prevent worsening of this situation is the unpredictability of the migration flight path (as well as the sheer size/territory covered).
The map below highlights the vastness of this territory
With urbanisation and development of critical infrastructure the world over, increasing numbers of Power Lines are creating a literal grid spanning every continent to provide critical power to communities and industry. This phenomenon continues to expand and roll out to meet the ever increasing population base. The North American landmass being vast has more than 500,000 miles of transmission lines. Distribution lines also play a part in bird wire strikes and by some estimates there are more than 116 million Distribution Poles in service.
Some authors believe Distribution Lines are more dangerous to Birds while others believe Transmission Lines to be more dangerous. The weight of opinion is probably on the latter. It is believed that the Earth or Ground wire is the main culprit in bird wire strikes. This is mostly due to its thinner size (being harder to see than the phase wires) and it’s elevated position. The Earth or Ground wire is necessary in Transmission infrastructure to help prevent lightning strikes and outages. Both Whooping Cranes and Sandhill Cranes appear to be extremely vulnerable to these Power Line collision, however, Whooping Cranes are perhaps more so, due to their larger body size and wingspan, slower wing beat and relative lack of maneuverability.
Whooping Crane migration involves only 17-20% of its annual activities, however, losses during migration may comprise up to 80% of annual mortality. Whooping Cranes are more likely to strike wires when traversing from their roosting sites to foraging zones. A potentially compounding factor is that these short flights typically occur near sunrise or sunset where visibility may be impaired. In any typical migration, there may be as many as 15 stopovers during the 4000 kilometer journey.
It has been observed in multiple studies and reports that Cranes react more often to marked than unmarked Power Lines. For Whooping Cranes, actually more wire strikes have been documented with Distribution Lines than Transmission Lines thought this could be biased due to the sheer volume of Distribution Lines when compared to Transmission Lines. Using Markers to increase the visibility of the overhead Ground Wire has been the focus of much study and research and appears to be the most effective way to demarcate Transmission Lines.
There are many different styles of products on the market including Balls/Spheres, Spirals and hanging devices or flappers, each with their own performance profile. The main advantage of hanging devices or flappers is there element of movement which is thought to dramatically increase their rate of perception. More studies are needed which directly compare these different devices for efficacy to all Utility Engineers to make informed decisions when selecting against the suite of preventative measures.