This one has me stumped.

I'm generally pretty good at identifying birds. I have never seen anything quite like this one. This bird looks like a warbler and behaves like a warbler. I imaged this one in Thorne Head Preserve in Bath, Maine, USA, on a pine tree collecting green caterpillars. The bird's colors are bright, orange on the neck and upper breast, green on the lower breast with black stripes on either side. Note the green and dark stripe through the eye. There is a hint of white on the wings. I only have this view from below. I have exhausted searches in my "Peterson's Field Guide to Eastern Birds" and "The Audubon Field Guide to North American Birds, Eastern Region" and internet searches. The original image is rather dark. I lightened the shadows and slightly increased the contrast in FastStone. I have not adjusted the saturation or hue. These values are Straight Out Of Camera. For this image, I used my manual focus Tamron Adaptall-2 Model 55BB SP 500mm f8 Mirror Lens and Tamron Adaptall-2 140f 1.4X Flat Field Teleconverter with attached Tamron Adaptall-2 Pentax K M Mount on Pentax K20D Camera, hand held, manually focused, Manual mode, Shake Reduction set to 700mm, ISO 400, f8 on lens, 1/125 sec, with available ambient light. My lens was functioning as a 700mm f11 Mirror Lens. This is a full resolution Large JPEG.