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
The susceptibility of birds to collision is also greatly determined by species characteristics, including their morphology, flight behaviour, phenology, and age.
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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.
© 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.
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A vast range of BFD has been developed over the years, including:
Spirals
Double-ended spiral devices with large dimensions (ca. 1 m long) but static and only visible to birds during daylight
Flappers
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
Spheres
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?
As part of the SafeLines4Birds project, several innovative tools are being tested to reduce bird collisions with power lines. These solutions aim to help birds see and avoid cables both during the day and at night, when visibility is low. While daytime markers will be tested to improve visibility for birds in daylight, additional solutions are needed for species that fly during low-light conditions, such as at dusk or dawn.
To address this challenge, the project tested a promising solution known as the Avian Collision Avoidance System (ACAS). This system uses ultraviolet light in the 380–395 nanometre range — a part of the spectrum that many bird species can see, but that is invisible to humans. This allows birds to detect and avoid cables in the dark, without creating any visual disturbance for nearby communities.
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ACAS had already shown promising results in the United States, where it reduced collisions for Sandhill Cranes by up to 98% (Dwyer et al., 2019). Building on this success, SafeLines4Birds carried out the first European ACAS trials in the winter of 2024-2025, at two locations considered high risk: one in France and one in Belgium.
These test sites were selected due to high bird activity and frequent collision records, particularly involving species vulnerable to night-time collisions. Target species included the Common Crane, Little Bustard, Northern Lapwing, Eurasian Woodcock and Eurasian Curlew.
Each ACAS installation included:
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2 to 4 UV lights (50W each)
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Solar panels and energy storage
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A control box and connecting cabling
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Mounted on the existing power line structures
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© James Dwyer
The system was automated, turning on at sunset, operating through the night, and switching off at dawn. Each unit illuminated a 200-metre section of power line to improve visibility for passing birds.
To measure the effectiveness of the system, a structured monitoring phase took place over 1 to 1.5 months during winter 2024-2025. The ACAS operated every other night, allowing for direct comparison between nights with and without the system in use.
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The results of this evaluation are expected in early 2026, following detailed data analysis.
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© RPS
© Mickael Potard
The project will also explore innovative methods for installing bird flight diverters (BFDs) using drones in France. This approach is expected to improve both efficiency and cost-effectiveness, particularly in areas that are currently difficult or impossible to access using traditional methods. By using drones, the goal is to double the daily installation capacity, allowing more devices to be deployed across a wider range of environments.
In total, the project plans to install 3,880 existing diverters (e.g, Firefly, Avisphere) along 60 km of high-risk power lines in France and Belgium. These installations aim to reduce collision risks for vulnerable bird species by an estimated 43% to 85%, depending on location and conditions.
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In particularly high-risk areas of France, medium-voltage lines will also be placed underground to completely eliminate the risk of both collision and electrocution. This measure is expected to benefit several priority species, including the Bonelli’s eagle, Egyptian vulture, Little bustard, Common crane, and Lesser kestrel.
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To evaluate the effectiveness of BFDs, the project will conduct field experiments at 10 sites across France and Belgium. These experiments will use observation technologies equipped with semi-automatic species recognition systems to monitor bird flight behaviour near power lines.
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​The data collected will provide scientifically robust insights into how birds interact with power lines, and how effective both BFDs and ACAS devices are in reducing collisions. These findings will help guide the future use of mitigation technologies on other sites and improve understanding of their impact on different bird species and habitats.
