I enjoyed listening to those bird sounds, too.
One of the banders who comes will sometimes play a bird song on her cellphone to get a response back from any birds that they get a glimpse of to verify when the real bird calls back.
Once there was a bird (I don't remember what species now) that would follow her on the ground after she played a bird song. He flew right in and landed near her feet. We thought it might be a male defending his territory against what he thought was another male. He was trying to chase her off. It was funny!