As I approached the river from the park, I heard the rattling before I saw them. A pair of Belted Kindgfishers was flying around a tree in the river, then began flying between that tree and a tree in the park nearby. The two I was watching were both females. Once I had a chance to look at the photos, I realized that one was probably a juvenile, with some brown spotting in the breast band. The other looked like an adult female.
I think there were a pair of these, but this is the one that was singing in the audio.