I wish i could say that I was photographing the Avocet on the ground and took the picture the moment that I saw the flying Avocet directly above the on on the ground. However, that's not true. I had just focussed the bird on the ground and happened to snap the picture the moment that the other one swooped in. It was total luck. Camera settings were shutter and focus in continuous mode, 500mm focal length, 1/2000 sec., f/5.6, ISO 100.
Equipment included Nikon D750, Nikkor 200-500mm f/5.6 lens, Induro Stealth CLT403 tripod, Wimberly WH-200 gimbal head.