Why Do Birds Fly into Power Lines? Is Poor Vision the Problem?

BIRMINGHAM, England, March 2011 — Power lines, pylons and wind turbines are easy for us to see, yet birds often collide with them. Do they not see them as well as we do?

Research suggests that collision with human structures is the largest unintended human cause of bird deaths, and some endangered species may even become extinct as a result. White storks are one example of birds whose numbers have been significantly reduced by collisions and power line electrocutions.

During a 16-year period, about 25 percent of juvenile and 6 percent of adult white storks (Ciconia ciconia) in Europe died each year from power line collisions and electrocutions.

To approach the problem, Professor Graham Martin of Birmingham University studied how birds use their eyes while flying. He found that some bird species can’t see ahead of themselves at times when they turn their heads to look down at the ground.

He also found that birds’ frontal vision, especially when the bird is hunting, tends to be tuned for the detection of movement, instead of spatial detail. So they may not always notice a stationary object ahead of them in time to avoid a collision. Also, some birds are physically unable to fly slowly, and when flying quickly it is more difficult to avoid obstacles. The problem worsens in low-light conditions or when it is rainy, misty or foggy.

“Armed with this understanding of bird perception, we can better consider solutions to the problem of collisions,” said Professor Martin in a release. “While solutions may have to be considered on a species-by-species basis, where collision incidents are high it may be more effective to divert or distract birds from their flight path rather than attempt to make the hazard more conspicuous.”

He concluded that it may be best to assume that birds are looking down or sideways rather than forward, so sounds or signals placed ahead of an obstacle may work better than one placed on it.

The study report appeared in the March issue of Ibis, which is published on behalf of the British Ornithologists’ Union.