Great catch. I've seen many people complain about these long lenses not being sharp or able to focus properly. The main reason is just as you say, it's actually much more difficult to hole these long focal lenses steady, even at fast shutter speeds than the shorter lenses. They are also heavy compared to the shorter ones, that makes it even more difficult to hold for any period of time, like I needed to capture these shots.
I normally use a monopod when doing wildlife photo's just because it's far lighter and easier to carry than a big tripod yet provides that much needed stability and fatigue reduction.
For these I didn't pull the mono out of the car, and instead leaned against a nearby tree for extra stability and used the built in image stabilization.
I didn't use it on these, but post-processing Topaz Sharpen tool and others can also work wonders to help correct some of that shake focus. These are all straight off camera with no post processing and actually just a copy/paste from the full resolution image to reduce the size for posting (I was feeling lazy)..