Kat, using Terramycin for something like a bird who has an injury may be what it's good for, if more than topical ointments seem required.
I had one hen who wasn't looking well recently; when I picked her up, we found part of a soft shelled egg protruding from her vent, and we pulled the rest out. Because we weren't sure what was going on inside, if she'd develop an infection in the oviduct, we gave her a couple of pencillin shots. If I didnt have anything else on hand, I would have used the bag of Terramycin I got way back when my first bird got bumblefoot. I found that this type of staph infection called for a stronger one than Terramycin, so the bag is still here.
For respiratory stuff, my policy is to cull, not treat, so no antibiotic, however strong, will be used if that happens her.
I just have no idea why anyone would give a healthy, just-hatched chick an antibiotic. Makes no sense.