If he’s alone loneliness and bullying can definitely be factors. Geese should be kept in pairs, but in the meantime I do know of folks whose situation allows them to keep a singleton by becoming the gooses’ “special friend”, with lots of interaction, treats (healthy ones), petting etc.
He may need to bathe too, especially in winter; I used to shower my ducks weekly in the wintertime, they washed, played, got Cheerios and parsley, and it was a great opportunity to check their body condition and overall health.
Water is also super important for waterfowl...thus the name...they don’t just need it for drinking, they literally can’t eat without it, that’s why their buckets etc get so dirty; what kind of waterer do you use? Can he get enough water to drink? Is he able to clean his bill and nares, (nostrils).
