It suddenly came back to me. There I was sitting at the Command and Control Station in my Bunker on the Old Eastside of town, looking out at my sparkling blue swimming pool, when a Tree Martin came in from the south, banked and dived steeply to the east to do a "touch and go" on the surface of the water before repeating the trick by completing another circuit and then disappearing.
I've never understood what they are doing. I've wondered about their being so thirsty that they will drink chlorinated swimming pool water, or whether they are picking up insects which are floating on the surface.
I first saw the phenomenon in January 1979, through the south facing window of my ground floor single room at the Professional Officers Quarters at the Alice Springs Hospital. The large ceiling to floor window, seen in the faded photo above, looked out on the hospital swimming pool, from what I always regarded as the best room in the house. Then [notice there is no need to say, 'back then' as 1979 gives that game away], the birds repeated their "touch and goes" numerous times. January in 1979 was very hot. It's been 42°C here [now] the last couple of days, but I remember a run of 14 days all of which were over 40°C in January '79.
There must be something special about being in an air conditioned room, with a south facing window looking over a swimming pool watching Tree Martins do their tricks in the heat of January. I'll have to think more on it.