This warbler caused a lot of controversy when we were there. It was initially identified as a Nashville, and mentioned to us by some other birders at Fort Jefferson. I think Nashville can be discounted pretty easily. But, the combination of field marks still didn't add up very well. The process of elimination ID came to by some very experienced birders in my group as well as the guide of another big tour group, was Common Yellowthroat. I came to Yellow Warbler as my ID (and likely a first-spring female) and it seems that is what most agree with from the photos.