Hi Angelika, sorry you've had to wait for a reply, where is your location and have you tried to contact any wildlife rescue centres for help? Here's somewhere to try initially ...
directory.helpwildlife.co.uk/
And another here ... pigeonproject.org.uk/.../
You could offer some mixed seed plus some defrosted garden peas and fresh water at all times!
Do you have access to a wildlife friendly Vet?
2013 photos & vids here
eff37 on Flickr