Thanks for the comments, everyone....
Which focus settings did you use, please?
AI Servo. Single (center) AF point (multiple point patterns never work for me, as I cannot control what part of the subject is in focus, and they fail miserably when there is a bg behind the subject other than a solid color). The AF case tweaks were: Tracking: -2. Accel/Decel: 1. AF pt switching: 0. I use BBF (back button focus technique). I have set the drive mode to Silent Continuous (4 fps) when I first was testing the camera, and have not changed it since. I love how quiet the shutter is in that mode. I rarely shoot more than a couple shots in a burst, so I don't need the super high speed machine gun mode (though I won't rule it out if I need it in the future).
I can't recall if I had the lens focus limiter switch set to full, or 10m~, though I've mostly been setting it to full range since I'm paranoid I'll miss a close-up opportunity.
I still need to experiment a bit more with the camera and AF settings to dial in what works best for me. Well, I guess I'll just have to trudge back out into the field for more testing. Sigh...
although this particular lens is way out of my budget.
Same here. So I got a loan
swans ... are not a difficult test of AF
Most of what you said is reasonable. Do consider, however, that subjects that are mostly white (or mostly black) can be challenging for AF.
Thanks again for the comments, everyone!