When birders talk about difficult ID issues, they never mention telling female Kestrels from "brown" (juvenile and adult female) Prairie Merlins. Yes, when seen in close-up photos, the two are easy to tell apart, but when seen at a distance in the field they can look very similar to each other. Trust me, I've seen some of the best birders and hawk watchers in the country make this mistake.

The flight style of Kestrels and Merlins differs, and the shape differences between the two are sometimes obvious, but the plumages can appear quite similar (Merlin on top, Kestrel on bottom). Next time you see a distant "Kestrel" that seems a tad stocky or is flying like a Merlin, take a second look. Hope this helps.