Light south winds made it a perfect day to get out on a smooth lake on the boat. While we had vague hopes for Long-tailed Jaeger or Red-necked Phalarope we had to make do with a few groups of juvenile Black Terns. We've had them out there both times we've gotten out on the lake this time of year. The blue sky background was harder to montage than I expected.
Next is two views of another bird which had richer brown scalloping to its juvie back feathers.
Black Tern (and Bonaparte's Gull) flocks often will do this erratic slip-slide downward. The Bonapartes frequently follow it by landing on the surface though I've never seen a Black Tern land in the water. I didn't notice what the stimulus for it was.
We saw a total of 24; this is the most I managed in one frame.