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©Ricardo Martins_Cranes+crossing+TL_edited.jpg

Reducing Bird Collision

© Ricardo Martins

What is bird collision?

Bird mortality due to collision with power lines can happen on distribution or transmission electricity grids. The main reason for collision is a bird's inability to perceive the overhead wires has an obstruction in the airspace upon approach. Thus, and although bird collisions can occur both with conductors and earth wires, they are most often a problem with the thin ‘earth wire’ at the top of high-voltage power lines.

Along with infrastructure features (wire diameter, pylon configuration and height), environmental factors such as topography, habitats, weather and light conditions can also influence the potential for bird collisions with power lines.  For instance, power lines that cross the bird species' regular migration routes can be especially problematic and the risk of collision with those infrastructure is a major cause of mortality for some bird species.

©Ricardo Martins_White stork carcass

© Ricardo Martins


The susceptibility of birds to collision is also greatly determined by species characteristics, including their morphology, flight behaviour, phenology, and age.

For example, larger, heavier birds with short wing spans and poor vision – and thus lower manoeuvrability - such as White Storks and Little Bustards, have a greater risk to collide with power lines. Moreover, species with a long lifespan, low breeding rate and/or which are rare or already vulnerable in terms of conservation status (e.g., Eagles, Vultures and Black Storks) are particularly at risk.

Bonelli's eagle © Vincent Palomares

© Vincent Palomarès

What are the solutions?

Placing power lines underground has been identified as the most effective solution to prevent risk of collision and electrocution for bird’s population. However, this is not always possible due to potentially greatly higher costs, or technical factors. Thus, when dangerous power lines cannot be put underground, marking the lines with ‘bird flight diverters’ (BFD) is one of the best mitigation solutions chosen worldwide.

A vast range of BFD has been developed over the years, including:



Double-ended spiral devices with large dimensions (ca. 1 m long) but static and only visible to birds during daylight



Dynamic devices in the shape of e.g., plates that rotate in the wind.

Some devices have reflective and luminescent parts to make them visible in daylight as well as at night to birds



25-cm spheres with one side in red and one side that lights up at night

It is important to note, that the effectiveness of these markers is still discussed and varies according to species, geography, and other factors (e.g., distance between markers).

What are the project actions?

In the SafeLines4Birds project, innovative approaches will therefore be adopted including the test of new Bird flight diverters, such as the American ultra-violet Avian Collision System Avoidance System (ACAS). The ACAS uses ultraviolet (UV) light in the 380-395 nm range to illuminate power line cables to make them more visible to birds at night. This approach leverages the fact that many avian groups are sensitive to UV light, a characteristic not shared by humans, including some bird species prone to collisions with power lines. Therefore, birds may see and avoid the cables without making the power lines more prominent from a human perspective.

In the United States, ACAS reduced Cranes collisions up to 98% without affecting nearby human residents (Dwyer et al., 2019). To test whether the ACAS may also be effective in Europe, ACAS will be deployed at two sites with documented histories of bird collisions, one site in France and one in Belgium. Each ACAS will consist of two to four UV lights, two solar panels, a power storage and control box, plus cabling to connect the components. All equipment will be mounted on the structure supporting the power line span to minimise the equipment’s footprint, and will automatically energise at sunset, shine through the night, and turn off at dawn. The partners within SafeLines4Birds will undertake monitoring and analyses to assess the effectiveness of ACAS. If proven effective, they will also document the species that are positively impacted by its implementation.

© James Dwyer ACAS_edited

© James Dwyer



Undergrounding ©Mickael Potard

© Mickael Potard

We will also explore innovative methods for deploying Bird flight diverters (e.g., drones) in France, enhancing both installation efficiency and cost-effectiveness. Our goal is to install more devices in various scenarios, including challenging access areas previously deemed impossible to equip. This approach aims to double the daily installation capacity, even in areas with difficult accessibility.

Moreover, the project also aims to install 3,880 existing BFD on 60 km, on the most dangerous sites in France and Belgium. This action aims to target high-risk areas for specific species, reducing the risk of collision by an estimated 43% to 85%.


In some cases, in France, medium-voltage lines will also be placed underground to completely eliminate the risk of collision and electrocution in particularly high-risk areas. This action will especially benefit the Bonelli’s eagle, Egyptian vulture, Little bustard, Common crane, and Lesser kestrel.

Finally, we will assess the effectiveness of Bird Flight Diverters (BFD) through observation technologies employing a semi-automatic system for species recognition during flight near power lines. Conducting experiments across 10 diverse sites in France and Belgium, our aim is to yield scientifically robust insights into bird behaviour around power lines and the efficacy of both BFD and ACAS devices.


The findings from these experiments will not only contribute to a comprehensive understanding of bird interactions but also inform the potential use of these devices on other sites for obtaining more precise information about specific species, habitats, or the effectiveness of newly developed devices.

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