Every last motion Gollum makes was Serkis doing it, including when he's jumping up on rocks and climbing down head-first. The animators certainly deserve credit for the facial expressions and the rest of the work of the digital costume, but he physically acted the part.
I don't disagree, but facial expressions is like 50% of acting if not more. That's why I said "Half of Andy Serkis' job portraying Gollum was done by animators"