Oh, Socialite, that's a pity... but from the pic the birdie looked really very young. In the place where I work, in this season we find birds fallen from their nests all the time. When they are this young, it is almost impossible to keep them alive. When they are a little older, i.e. they are still a little "round" in shape but have already almost all their feathers, the chances to make them survive are more. A colleague of mine is specialised in bird rescuing. When we find them, we put them in a cardboard box, and then first thing she feeds them a special food mix for young birds (basically a thingo that she processes with water to form a sort of cookie dough) that she puts in their beak keeping the whole bird firmly in her hand. Knowing that emergencies happen all the time now in spring, she always keeps a small amount of this food with her - especially at the office. Then the bird must drink some drops of water - I think the main danger for them is to die of dehydration) and then she puts them back in the box. This every two hours. Then as soon as she can - but sometimes a day or two later, because she is very busy - we bring them to a bird shelter, and they continue from then on. In this way we have rescued dozens of birdies, but many also succumbed either from the shock of the fall or because they were too young. None the less, you probably did the best you could do. It is really very difficult to keep them alive...
