Different Sort of Visitors to Jones Beach  

I finally caught up with the late lingering Gull-billed Tern at Jones Beach. I wanted to get pictures, as I suspected that in late September, it would be in a plumage that I don't have. And indeed, it shows a diminshed amount of black on the cap, and darkened primaries. It's hard to find pictures to compare to, but I'm leaning to adult rather than juvenile. Similarly, Empidonax flycatchers are confusing enough as adults..Come fall, anything seems possible. I see what looks like a buffy wash on the belly. But surely, it must be yellowish? As in Yellow-bellied Flycatcher? But it doesn't strike me as that, as the upperparts aren't particularly greenish.