Not sure

I found this small bird sitting in the middle of a parking spot. Olive green on the outer part and yellow belly.It allowed me to pick it up. It seemed in shock at the time but as soon as I got it home,I put it an extra bird cage I had and it just sat there. I don't know what it eats or if I should even keep it. I was a little worried because the temperature just dropped to the 50's and I think this was causing it to not move. I didn't want a cat or grackle to come and eat it. It has started to fly on the bottom of the cage and sing a little. I am located in South Texas (Corpus Christi)