Chaffinch in hiding

This was taken on a day when the wind was from an Easterly direction,and so cold that the Chaffinches took shelter among the branches.I had doubts that the A/F system would be selective enough to focus on the bird,rather than the confusion of twigs!But I needn't have worried!Here is the result to prove it!
If I had known for sure I would have selected a larger aperture to take the branches out of focus more?

Nikon D800 +Sigma 150-500mmO/S APO @DX =750mm, F13 @1/160 sec. ISO 250