This may be the case with the quail I once had.
I had bought ten quail to start raising for eggs and meat. I ended up trading for about thirty more. I went through and selected my males that I wanted to keep for breeding stock and processed the rest (kept all the hens).
They began laying and I was beginning to collect eggs for incubation. Well, I went out one morning to find my gate wide open with two birds headless in the cage and the rest, GONE.
I had no idea what happened but suspected a coon, but no chickens were bothered and they were more accessible.