Here are some more images showing focusing in cluttered and/or low-contrast scenes. The two images of the owl (a Great Grey Owl) are good examples of images taken on a dark, dreary day, in fairly thick forest (ISO 800, F8, 1/100 and 1/200 shutter speed). I had little or no trouble with focus hunting.
None of these images are cropped; they are all just downsized for web display. The only one brightened is the nparula1_sm.jpg - it was so dark that it was hard to see what I was trying to show. All have the original EXIF data. All are taken with a tripod-mounted E-520. None of these shots are one-shot wonder lucky shots, with blurred images before and after. Most were taken in short bursts of 2 or 3 images, and the images on either side were similarly in focus.
As in my earlier album, I am not saying that these are good pictures. They are pretty poor, in fact - I deliberately chose images that isolated the bird from a clutter of branches, etc. Several are actually not in perfect focus, but this is more the result of camera shake, bird movement, and the other problems inherent in high-magnification photography. None were fooled by the poor conditions and the lens was not hunting back and forth.
I do think that using a tripod (plus the Manfrotto 293 bracket - see my review here) helps a lot, not just in keeping the setup steady, but also in allowing you to avoid accidentally moving your focus point to something that will cause the lens to start hunting. You obviously have to keep your focus point on the animal as it moves. Hopefully, it will emerge into a more open area and you can get a good shot. In fact, often I am taking pictures even though I know the bird is surrounded by garbage, just to maintain the focus point, so when conditions improve, my focus will be in the ballpark.
Click a thumbnail to see a larger image.