Hello Hans and Oscar
What made me think that this bird did not fit 1cy Herring Gull was e.g.:
- Solid dark centres and with white edges on the very worn tertials. Most Herring Gulls in Denmark at this time (mid-September) show rather fresh tertials.
- Rather many mantle feathers have been replaced already which also is somewaht early for Herring Gull imo.
- Whitish head with some darker markings around the eye.
- Very dark centres to the larger and medium coverts on the upperwing without the more chequered pattern that most often is found on Herring Gulls.
- Elongated jizz with a seemingly rather small head and "push-up" breast.
- Blackish tail-band
- Very dark upperwing without an obvious pale window to the inner primaries.
I guess all these imo diverging characters could be found on a sample of Herring Gulls but not on a single bird, I would think.
Best wishes and a happy new year
Rune Sø Neergaard