I’ve been helping with some surveys in the Rio Grande Valley to document bird movements at proposed power line crossing sites, so I was even more interested in a recently published paper in the journal Conservation Biology on some birds’ inability to see obstacles in their flight path. An article from BBC Earth News summarizes the paper well. I fist saw this topic in a post on 10,000 Birds.
Cranes, storks, and raptors are prone to colliding with power lines. While power lines are thin and may be hard for birds to see against the sky, this new study suggests that these birds have blind spots, making it physically impossible to see any danger ahead of them.
Birds with long bills have very good eyesight directed at the tip of the bill, but have large blind spots elsewhere. Martin and Shaw (2010) show that for cranes and storks, a 35° and 55° tilt, respectively, is enough to render the bird unable to see anything in front of it. Although these birds look straight ahead while flying, they often turn their heads to look for feeding and roosting sites. Power lines that are built over wetlands, marshes, and fields (excellent bird habitat) can be particularly lethal.
Hawks also have focused binocular vision and blind spots and are also prone to power line deaths. Habitat under power lines supports many raptor prey species and hawk intent on catching a meal might hit power lines on their descent or chase.
This research indicates that adding color or markers to lethal hazards such as power lines and wind turbines may not make a difference if the birds just can’t see them.