It’s really great that you’re putting in so much effort to look after this little guy. If he makes it to a rehab place, please let us know - I’d like to make a donation.
Almost sounds like your Owl was confiscated from someone that had it as a pet.
If that is the case, it may be afraid of outside and non human company.
If so, you will need to try transitioning it, can you build it a little outdoor flight cage?
Those little guys can eat crickets, beetle larva, grub worms, pinkie mice, small lizards.
Be even better if you can find a rehabber that has other owls of that kind so it can learn from its own kind and be released with a friend.
The OP is in Mexico. The International Wildlife Rehabilitation Council (theiwrc.org) has a link to an international list of rehabilitators for Canada and Mexico. Unfortunately, when I checked just now it was closed for repair. Perhaps local wildlife authorities know of rehabilitators in your area. Vets don’t usually have the flight cages necessary for rehabilitating wild birds. And in the USA veterinarians do not have blanket permission to possess “migratory birds” (basically all species that nest in USA) except briefly, for stabilization. After that the bird must go to a permitted wildlife rehabilitator. Mexican laws may well differ, but there is still a good chance that vets know about rehabbers. It’s worth asking.
I think Crazyhorse was also talking to a local Audubon Society person, who may well know of a local rehab person who could help. Unfortunately, my contacts in Mexico are much farther North. I guess I’ll ping them anyway and see if anyone knows anyone who knows anyone. Can’t hurt.
Thank you all for the help and suggestions. Unfortunately Woodsy didn’t make it. They now think it was rickets or another disease caused by long term malnutrition and/or lack of exposure to sunlight that caused the unusual curvature of his leg and his eventual demise.
The veterinarian, wildlife care manager at Audubon and director of the International Wildlife Rehabilitation Council all were contacted prior to my first post, and helped heroically to search for a rehab anywhere within the state and offer advice on his care in the mean time but to no avail.
I work in animal rescue and rehab (but with a very different species) and am sadly accustomed to hopeless cases arriving at our doorstep, but this one really got to me. Mostly because of my lack of knowledge of the species and his apparent outward good health and appetite, I thought this wasn’t even close to being hopeless. But under those fluffy feathers was essentially a bare skeleton. His size was surprising to all involved, and that too was a result of lifelong malnutrition.
It is almost certain he was held in captivity at a tourist attraction or other animal exploitation venue. We will never know because the process is done completely anonymously; I don’t get to know where he came from, and they don’t get to know where he went. I will report his death to the wildlife agency that brought him in the hope that if they do have someone to blame for this, harsher penalties will be given to them.
If there’s any moral to this story for a US/UK audience it is never pay anyone to let you pose for a photo with a wild animal when you’re on vacation in Mexico. It’s an epidemic problem in this region and if they couldn’t make money doing it they would stop.
Wow, sad update. Again, you get huge props for doing what you did. And I agree, animal tourism is almost always awful, if only people would do a little due diligence. RIP, little owl.
I am sorry to hear it. Thank you for what you were able to do for him, and thank you for the update.
Poor Woodsy. I’m glad he had a little cat food in his life. 
Many thanks for your earnest and very humane efforts, Crazyhorse, and for telling us all about it here. So sorry it didn’t end well for the little guy.
Sadly, this is not an uncommon scenario. It’s what I implied when I said “…provided the starvation didn’t cause significant organ failure” at Post #38 above.
Crazyhorse, thank you for your efforts – both on behalf of this owl, and the other wildlife that you deal with. We all know that there are no guarantees, but we keep trying.
Yes, kudos to you Crazyhorse for the work you’re doing and what you attempted yo do here. I’m sure it has its rewarding moments, but I think I’d find rehab work wearing, if only due to the inevitable failures.
Sometimes things go right. If I manipulated my tablet and my YouTube correctly this link should show a recovered bald eagle being returned to the wild. I don’t know how to make it a hyperlink in Tapatalk. It’s only 15 seconds long and I don’t think anything in it requires two-click isolation.
Sadly that seems to often be the case, you lose many more times than you win.
I help with a local rehabber when i have time and i seem to bury more than i set free.
Not all is due to humans, a lot is mother nature and natural selection at play as well.
We do a good share though