Marmoset, I don't know, but I'm so glad I'm not the only one who stresses about this. When I was outside late at night feeding the stray last September, I heard what I could have sworn was a cat mewing. After that, I heard it a few more times. It was a little mew, then quiet for a few minutes, then another mew. I went around trying to figure out where it was coming from and trying to lure out the kitty. When I called softly, the mewing would stop. Then I'd hear it again. One time, it seemed to be coming from the ivy-covered ground just past my property in the neighbor's yard. But it was about 2 am, and I couldn't really go tromping on his land. Another time, it seemed to be coming from across the street. The stray didn't react to it at all, but then again, she was so emaciated and weak that she didn't react to much of anything other than food. And since she had shown up in that state, I was really worried that there were more kitties somewhere who were too weak to move. I never saw any kitties, though I did hear the mewing a few times after the kitty was no longer outside. I haven't heard anything in the past couple of months, so I'm hoping that it was maybe a baby bird.
But I'd love to know for sure.