I only took up bird and wildlife photography 3 years ago. I have been waiting for the D400 to replace my D7000, but have now decided I've waited long enough. I've only had the D800 3 weeks, but already I have decided, apart from feeble fps, it will do everything the D7000 does and possibly the D400 could too, apart from fps. All is not lost fps wise, as I now also have the MB-D12 grip and on DX mode the D800 will do 6 fps, plenty for me.
If the sun ever appears in the UK again and the day stops looking like the night, I will look forward to getting out and about to do some more D800 work.