You do not need to put down old birds who are dying to end their suffering. Unless they are sick or injured, the process of dying is relatively peaceful, though it may be disturbing for some of us to see. I have been lucky/sad enough to see several of my old ladies go simply from old age after a good and happy life. To whisk them away and cut off their heads or take them to a vet- whatever, would make her last moments frightened (especially since as this is happening they can't see well or understand what is moving them). If they are peaceful and simply still and quiet with their companions I only make sure they are warm & dry & not being bothered. A hen who had been on the mean side once was harassed by the others as she was going and I had to step in, but once the oldest "top" hen was dying and the others- I swear on my life- my mother saw it too- took turns standing or sitting next to her & even supported her from falling sideways until the end. She just quietly ended her life surrounded by familiar surroundings and friends. Wouldn't we all like to go that way? I felt those hens deserved their process way more than I deserved to be spared the sadness it caused me to watch. That being said, I have had two hens put to sleep who had terrible injuries that were causing them pain and from which they would not recover.