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Friday, April 1, 2011

Why birds collide

Ever wonder why birds smash into objects when flying? Graham Martin of Birmingham University did. He recently published a study in the journal IBIS (guess what that journal specializes in) exploring that topic.

According to Martin, the tactics we use to make obstacles visible to us simply don’t work on birds. For one thing, birds may spend very little of their flying time looking straight ahead. Instead, they may be scanning the ground for prey, or looking around them to evade predators. Unless they live in deep forests, they may have little evolutionary experience with encountering obstacles in mid-flight. Even if they do spot such an object, they may have difficulty interpreting its significance, especially if their visual acuity is not sharp directly in front of them. And finally, birds may not be able to process the stimulus of an unexpected object in their path quickly enough to change air speed or course.

These are not trivial problems for bird populations. It’s estimated, for example, that up to a third of some endangered species perish by colliding with power lines. Calling attention to such obstacles with markers like flapping flags that would be obvious to humans does not seem to be helping the birds. Martin suggests that signals on the ground that divert birds from approaching obstacles may be more effective. Unfortunately, apart from avoiding known flight paths, there doesn’t seem to be that much we can do to attract the birds’ attention to the problem.