Thank you for your reply. I, too, was wondering about the breeding possibility as I have a Toulouse goose that feeds in the same vicinity as the Sebastopol, but usually its the Sebastopol that is the aggressive one. I suppose late February is getting close to breeding time, although it's been so cold here, it doesn't feel like spring will ever come. I gave the goose a bath, and washed the spot. His feathers were damp extensively under his upper wings before I started and very smelly. I then put him in a pen in the barn. He hates the isolation, (except for the cats). We'll see if he gets better.
I've had my Sebastopol for several years and this is the first year he has had discoloration on his back. There are fewer feathers here, but the skin is not broken, just somewhat red. However I do feel this is a source of irritation. Has anyone seen this before?
