Thanks guys, I wondered if it would be worth it carrying the 100-400, and it sure was just for that 3rd shot (but also for the bears).
One thing I've noticed on this site is that many shots (mine and others) seem softer than the web versions do on my computer. Is there compression applied when we upload? Part of what I love about that 3rd shot is the sharpness on the bird is perfect - you can make out lots of detail in the feathers, but it doesn't show here.