In troubleshooting my feathers, I removed all the lights from my scene and have found that they are glowing brightly. The culprit is the body base texture (seen on the left) that's being instanced for the feather particle system. When I unplug it from the rest of the texture everything goes dark, as it should without scene lights! BUT it can't be just that texture, because it's applied to the body itself, which doesn't glow. I'm missing something.
What you are doing is putting a (yellow) Color output socket directly into a (green) Shader input socket, which makes no sense at all, so Blender (since 2.81-ish) inserts an Emission Shader in between (behind the scenes):
