I could just feel the faster focus speed with my 300 mm Nikkor...
I've never seen or heard of a white heron, nor have I ever seen a heron dive for a fish from the sky but perhaps these birds do, and if yes, I know you'll accomplish your mission.
It's focus is certainly quieter than the Tamron Christina
There's a few of the white ones here and from my investigations some info is given that the white ones are mutants of the common grey reef heron and to confuse it more some times referred to as Egrets.