Clearing out my grandmother's house and have found a fair few old fashioned eiderdowns. They are in good condition but need washing and are pretty ancient. I certainly don't want, need or have space for them. Recycling centres say no duvets, which I guess includes things like eiderdowns.
I paid well over £100 for this beauty on Esty. If your eiderdowns are too big for your washing machine, take them to a laundrette where there will be larger machines. Wash and dry them in a duvet cover for protection.
Other posters saying don't give to animal shelters. (I have but there might be different rules in different places.). I've also noticed a lot more rough sleepers this winter - I'm sure they would appreciate extra layers instead.
Our local community centre collects them to give out to the homeless. I only found out by taking some donations there for the food bank. You may have similar near you or I think the Salvation Army can also take them to give to those who really need them.