Luke warm is not going to do. Too cool and he can get yeast or a number of problems like slow crop. Too hot and you can burn the crop. As mentioned, care must be taken not to aspirate the baby. As you look at the face of the bird, you enter with syringe from the right side crossing over towards the left. The type of syringe is important. Some push too quickly. You need a thermometer, and the formula{what kind do you have? it should be Zupreem embrace plus-it has extra fat for baby macaws} needs to be the consistency of applesauce. Use the thermometer and warm the formula to 108-109 degrees F. Keep it at this temp by putting the formula in a bowl, and that bowl in another bowl with warm water under it. Keep stirring it and test with the thermometer.Do not heat in a microwave. Clean up the baby by wiping him off of any formula afterward. Do not give straight water. Do not add anything to this formula, except water. You need a gram scale, and weigh him daily. He needs to get 10% of his body weight at each feeding. Is he fully feathered?Can you post a photo so we can help determine how old he is. He needs to be kept warm, about 85F if not. He should be in a brooder, or a makeshift one can be made with an aquarium, with a heating pad under on ONE SIDE if he is not feathered yet.
He really should be seen by an avian vet, to make sure he is ok.I sent a PM with my ph number if you need more support I am here for you. Thanks for caring for him.