Thanks everyone, really appreciate the encouraging feedback.
To share how I managed these shots:
I'd been walking by the river earlier in the afternoon with the dogs, and it was obvious the hormones were rattling about with the male ducks, they were chasing female ducks all over the place, but I noticed that when the female(s) took off (with a couple of males in hot pursuit), often they were taking similar flight-paths, and landing in roughly the same place on the river.
So I went back later on the afternoon (when the sunlight was lower and better), hoping the males would be as frisky as earlier, luckily they were.
I set myself up next to the river, with the sun (and wind) behind me, the ducks would take off, occasionally loop over the river, and come into land at an angle in front of me, then curve round to land into the wind.
I was able to start tracking the duck as he started his descent, aiming to shoot him just before he slowed right down to curve in to land.
This way, I had the side of the duck lit from the low sun, the duck had slowed a bit so was easier to keep focus, and had the river as a backdrop.
Technically, I used a 200 mm F2.8L lens (which can autofocus lightning fast) with a 1.4 TC, I shot on a1 servo , with auto ISO, set the shutter to 1/1600 sec, aperture at F5.6 to give a bit of a safety net with DOF, and let the ISO take the strain, but as I knew the light was good I realised the ISO wouldn't be excessive. Exposure was evaluative as the light was fairly even across the frame.
Post processing -a minor crop, usual levels adjustment, USM etc, and in the first image had to clone a rather large poo the duck was engaged in while coming into land.
