Those are MEGGA shots Neil. Could I be cheeky and ask you your in camera settings. You can PM me if you like, no worries if you don't want to share them. Neil.
There is nothing secret about setting up the D810.
I have 21 focus points selected in Continuous AF Mode.
Manual Exposure Mode and iso set to keep Shutter speeds around 1/2000th second.
I like to hand hold to be able to get on the birds faster.