Also, keep in mind the area where these birds were found, if there are areas where people can be spraying pesticides or chemicals...the birds are being fed the insects being caught by mom and dad.
I worked as a veterinary technician for a while. The case I will never forget is one where I had to stop and tell my vet that she was wrong on her diagnosis.
A dog had come in with coughing up blood, lethargic and bloodshot eyes. After taking down some info I asked about the dog's habits or any changes in diet.
"He used to catch and eat rats. I stopped that tho. We put bait in the garage where he can't get it"
The vet diagnosed him with possibly severe kennel cough. Told me the bait was in the garage. The dog can't eat the bait.
"What keeps the rats from eating the bait and then leaving the garage?"
Eyes wide, she ran back in the room and asked the owner about it again. We added the coagulation test to the blood work and did an ultrasound.
The dog was bleeding internally from eating the rats that ate the poison. He was put down after the blood work came back as him being too far gone.
It's pretty easy to keep a couple rats or mice to breed if absolutely necessary. But feeding wildlife to an animal that hasn't been exposed to wild conditions is a bad idea. Especially when they're kept in a small area that can easily lead to constant re-exposure to bacteria or parasites