Birds may crash into super-clean windows and get hurt

Glass that allows light to pass through unhindered stops birds abruptly in full flight, which can lead to fatal injuries. — Agami/T. Muukkonen/blickwinkel/dpa

Windows that are too clean and too transparent are a danger to birds. All too often they don't see the glass that allows light to pass through unhindered, but stops them abruptly in full flight, leading to fatal injuries. Large windows are a particular problem.

One simple solution is to clean them less frequently, as the accumulated dirt can be seen by the birds, which then realise there's an obstacle.