Brother M. sent me this picture of what I was describing yesterday:
It kind of highlights the difficulties of lens choice; to capture the people, the birds become invisible. If you blow it way up, you can see groups of cranes and ducks flying near the horizon. Also the stubble is full of grey blobs; each is a sandhill crane. Brother M and I have our binoc's trained on an absolutely enormous flock of geese coming in near the levee, a couple of hundred meters away. The tall guy at the back was the naturalist who was leading the workshop. I forget his name, but he was able to name each kind of goose and duck, some even as tiny, distant silhouettes.