My neighbor altered me to a baby bird (hatchling? / nestling?) on the ground in his front yard and was in immediate danger of being eaten by cats. In fact the parents were swooping down and attacking the cats to protect the baby for hours. Eventually they tired and he had to pick the bird up to keep it from being eaten by the cats. He looked for the nest, but could not find it, and the parents had flown off. Perhaps the cats had originally knocked the nest over? After some time of trying to reunite the baby with its parents (who were nowhere to be found), he asked for help taking care of it. I also tried to find the nest and the parents without success. We considered creating a new nest/basket and hanging it on the same tree, but with the number of cats around we thought it might be dangerous.
Eventually, I reluctantly brought it in, made a makeshift bed, and brought it to my in-laws nearby who had a nice garden, and more importantly, time, to watch over it. It took about 2 weeks of feeding it worms from the garden and bringing it outside every day, but eventually it happily flew away to find food on its own, and we have never seen it since…