I saw Eastern Meadowlark last summer, and it was definitely not what I saw yesterday on the islands. The bird was behaving more like a warbler, skulking into the dense thickets, plus the bill was totally different, stout and short, the llimit between the yellow on the breast and the lower belly white was really neat. Furthermore, there was no sign of black on the breast.
So I really think this was a YB Chat after all, even though I had no previous experience with this species. But it is very frustrating that I could not relocate the bird.
best
Mathieu