A study done by Kazuhiro Wada (neuretuologist) interbreed zebra and owl finches and looked at gene expression of the offspring. About 10% of the gene expression in the song nuclei were expressed differently between the two species, which could explain different songs in different birds. Another study was done where baby zebra finches were raised with adult owls to see if their songs would be influenced, but it was not. They did mimic the owls partly, but there were still characteristics of their own species song. This can suggest that genetics play a role in different songs.
I do agree and believe the research that was conducted is correct. I think it is extremely fascinating that many birds have these characteristics because of genetics. I see it as a natural instinct, rather than a choice they are making. Sometimes species do not need to be taught to do something, but it is because of what they are and I think that the research conveys that.