I’m not sure what it could be... I have pheasant feathers and they’re different markings to this.
it has a very silky straight side on the right of it.
found near an owl box but no pellets around it so I don’t think it’s a used owl box.
Take a look at Tawny Owl on Featherbase HERE to see what you think. You can click on the individual collections to enlarge the images. I'm no expert so it's just a suggestion.