ML techniques are leading to some interesting work in determining this. Here's one such example https://journals.plos.org/ploscompbiol/article?id=10.1371/jo... Female zebra finches do not sing, only males do. I'd imagine that if bird song is high on communication, it would be seen in both sexes (and there are song birds where females sing, but not studied as much as far as I know.) tldr: still unclear, but new techniques give us hope we can answer