Way too big for skylark. Try pheasant.
Well, here's the featherbase site for you to look through: https://www.featherbase.info/uk/species/Scolopax/rusticola
I've linked to the woodcock page since some of the feathers from that look like likely candidates:
https://media.featherbase.info/images/99d01ded-2b82-4287-bede-6424fdfce50c_full.jpg
If you think that's not close enough, look through the entries for other birds of a similar size. The feather didn't really match anything on the pheasant that I could see but it's certainly a closer match for size.