The yellow-rumped warbler has some pretty distinctive markings. So once you get a good enough view, it is easily identified. The key is getting a good enough view. It tends to move around a lot. It's a lot harder to aim binoculars at where you are looking - and have them be focused - than we had realized. We're getting better but it is still a challenge. We spotted this one at the Magic Hedge on a rainy Sunday morning. I have found that patience helps -- eventually the birds do take a rest between flitting/feeding fits and even seem to pose for the camera.