Why Do Birds Collide with Manmade Objects?
Birmingham study suggests that birds may not be looking at what obstacles are straight ahead and some of them may not be able to slow their flying speed.
From office block windows to power lines and wind turbines, many species of bird are prone to colliding with large manmade objects, many of which appear difficult not to notice to human eyes. A study published in IBIS outlines a new approach to understanding how birds see the world and why they find pylons and turbines so hard to avoid.
The problem of bird collisions is a serious concern for conservationists. Research suggests that bird mortality caused by collisions with human artifacts is the largest unintended human cause of avian fatalities worldwide.
Collisions with large and prominent obstacles may even threaten the survival of endangered species. In Europe over a 16-year period, it was estimated that approximately 25 percent of juvenile and 6 percent of adult white storks Ciconia ciconia died annually from power line collisions and electrocutions.
“From a human perspective it appears very odd that birds so often collide with large objects as if they don’t see them. It is widely held that flight in birds is primarily controlled by vision, an idea captured by the phrase ‘a bird is a wing guided by an eye,” said Graham Martin, a professor at Birmingham University. “However birds live in a different visual world to humans.”
To get a clearer understanding of how birds view the world Martin turned to sensory ecology, a field of study which investigates how sensory information underlies an animal’s behavior and its interactions with the environment.
“Previously most proposed solutions to bird collisions only consider a human perspective of the problem,” said Martin. “Put simply, it has been a matter of finding a solution to bird collision problems based upon making the perceived hazard more conspicuous to human observers, not birds.”
The research reveals that a subtle set of interrelationships exists between a bird’s visual capacities, the interpretation of sensory information, and the behavior of birds when flying in open airspace.
“When in flight, birds may turn their heads to look down, either with the binocular field or with the lateral part of an eye’s visual field,” said Martin. “Such behavior results in certain species being at least temporarily blind in the direction of travel.”
Martin also explores how avian frontal vision is tuned for the detection of movement, rather than spatial detail. When a bird is hunting, this detection may be more important than simply looking ahead into open airspace.
Birds also have a restricted range of flight speeds, for many birds it is simply impossible for them to fly slowly, making it difficult to adjust the rate of information they gain if visibility is reduced by rain, mist, or low-level lights.
“Armed with this understanding of bird perception, we can better consider solutions to the problem of collisions,” said Martin. “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.”
It may also be best to assume that birds are more likely to be looking down and laterally rather than forward, meaning a signal placed on an obstacle also may be missed. Alerting sounds or signals placed a suitable distance from the hazard may be more effective.
IBIS is the international journal of avian science and is published on behalf of the of the British Ornithologists' Union. The journal publishes original papers, reviews, and short communications reflecting the research activity in ornithological science, but with special emphasis on the conservation, ecology, ethology, and systematics of birds.
The U.S. Fish & Wildlife Service developed a committee in 2007 to develop an approach for protecting wildlife and its habitat in areas where wind power farms are being considered. The committee released a report to the Secretary of the Interior one year ago. To access the recommendations, click here (pdf).