I was interested to read the observations of David with regard to the behaviour of a group of hirundines over a lake he was visiting. Possibly it had nothing to do with bathing but more to do with feasting on a hatch of emerging fly from the lake. The rain often hinders the emerging nymph from escaping the surface tension it’s unable to dry off quickly thus becoming a sitting target for both fish and birds. The largest group of suspects are probably the chironomides commonly known as buzzers (these are not the biters) or possibly one of the sedge flies. A fall of terrestrial flies brought down onto the lake are also a possibility ‘flying ants’ or the ‘daddy’ both being significant food items on the menu of many fish and birds. I’m sure Mike Hayward with his piscatorial prowess could write a paper on the subject; fishermen and entomology theories go hand in hand J
Tony Clark