Evidence of bird activity was noted in an attic of a recent home inspection on Lopez Island in the San Juan Islands.  When you see feathers in your attic area, you likely have a soffit vent that isn’t properly screened, or the screen has become damaged allowing birds, and possibly vermin, into your attic area.  I recommend taking a peek into your attic annually to look for obvious signs of birds, vermin or mold.  In this way, you can deal with the issue before it becomes more significant.  Bird feces running down the exterior siding of a home may also suggest they’re getting into the attic, and the soffit vent location that likely needs to be re-screened with mesh screening.  Don’t just block it off, it’s important to keep the attic well ventilated as blocking the soffit vents can lead to mold growth in the attic area.