While out on a regular early morning (c.05:25am) walk with the dog I made the following observation. After I leave home, I pass close to some residential properties, where there is constant artificial lighting, here early morning birdsong is well underway. When I reach the lane and walk-up the hill, there is only natural light, the birdsong has not yet begun. I return along the same route, 20 minutes or so later, the birdsong is just getting underway in the naturally illuminated lane.
An example of how light pollution affects the birds natural daily cyclic rhythm.
