If you all haven't figured it out by now, I tend to shoot things when they're doing things
Anyhoo, here are stuff I've been working on recently. Arranged in order of increasing difficulty for me:
1) snowberry clearwing hummingbird moth (sex unknown) - 300mm
2) ruby-throated hummingbird (female) between flowers - 300mm
3) tree swallow (female) at full clip - 300mm
4) tree swallow (female) just before veering away from me - 500mm
5) dragonfly (sex unknown) stalking flying prey - 300mm + 2x TC
The 300mm f/4L IS is easy to focus fast and precisely. But the dragonfly was the most difficult catch because of the addition of the 2x (i.e. long, slow, dark) and because the dragonfly buzzed by extremely close in this shot and I almost couldn't track it at that distance.