Are his feet swollen and toe tips black? That looks like frostbite. I would bring him into a cool spot in the house. Offer him water with electrolytes or give him poultry NutriDrench 3 ml by mouth. Offer him some wet chicken feed, chopped egg, rinsed tuna, or chopped meat in small amounts to tempt him to eat. Encourage fluids orally with a small cup to his beak, and dip it in a time or two. His toe tips and nails may eventually fall off, but he will still be able to get around okay. Iodine or betadine on those black toes can help.