I volunteer at a Wildlife Rescue organization in the area. It has been awhile but I have helped in the bird rooms with feeding and I know that we gave fluid of some sort to the birds that age. You may want to contact a similar organization for information on what to give the little fellow. You can Google Wildlife Rescue and Rehab in Kendalia Texas for their contact information. They have a 24 hr hotline and might be able to advise you.
You are a good person for saving him.