I was looking into a proposal for another wind farm in Neath from the point of view of possible bird collisions, and came across this piece about research by Professor Graham Martin of Birmingham University's Centre for Ornithology. It seems that birds look down, or sideways, rather than in front when in flight. "Such behaviour results in certain species being at least temporarily blind in the direction of travel," says Dr. Martin. He 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.
So the measures so far adopted to make man-made objects more noticeable to birds may be ineffective. Placing wind-farms off known routes would prevent deaths among migratory birds, but not of those foraging. Static markers, no matter how they may appear to human eyes, would not be good enough. Perhaps devices which flutter and emit an alarm sound would do the trick? More research is clearly needed, because pylons, power-lines and wind-turbines are only going to increase.