Little Blue Herons can be very difficult to catch in flight. It’s not that they are any faster, or erratic, than other similar birds. It’s the color.
Unless at the right angle, or the sky is perfect, they are too dark. Their bodies are almost monochrome.
Most birds I will shoot with the sky as the background and lighten/darken later at processing. The Little Blue blends in with the surroundings too well. I tend to skip many opportunities to photograph them.