I had this problem with a few birds that hadn't fed in so long they were too weak to take food, I mixed Tropican baby bird powder (petsmart in canada) into a slurry and dribbled some into the corner of their beaks so they instinctually swallowed some - it has been enough to perk them back up, and you can do it with their poultry food if you have a weak quail or chicken......>
<.... I use a needle less syringe and eventually they will look for it and you can thicken it up for them to gobble down. For hatchling baby birds I find around here, I make the Tropican into little footballs and let them grab it from something blunt :)
Was that your hatchling, in your avatar? It looks like a starling hatchling.....I looked after one once..sadly he didn't make it...:(
My avatar is a hatchling sparrow that fell from our roof, raised and rehabilitated him back into the wild :) thank goodness he landed on our garage first, otherwise he probably wouldn't have survived :/ sorry to hear about your starling! Sometimes they are too far gone ;(