perhaps not entirely relevant but maybe linked? When I was working at an airfield in Germany in the 80s we had new radar installed. Very pleased with our new kit, except every morning we got bllooms of primary radar returns... someone noticed these appeared around sunrise and last 15-20mins... then it was noted they were radiating out from the same points every day, expand and disperse. When the origins of the blooms were plotted they were found to be a series of lakes. Scientific explanation... waterbirds taking off after having roosted for the night.