Music is simpler than most band class teachers would have us believe. Every sort of musical scale, Western and non-Western, is harmonic. What that means is every note, or acoustic frequency, is a whole number multiple of some base note (or frequency). So, if you have some note x, the next highest note is simply 2x. The next highest after that: 3x. And so forth.

When the researchers analyzed 71 different songs produced by the hermit thrush, they found that most of them (57) used the same musical math that we do. It's possible that female hermit thrushes pick their mates based on their ability to sing according to these scales. It's also possible that they (like humans) find it easier to remember melodies made by these rules, and build their songs around them so they're easier to learn and recognize. We don't know that there's something inherently pleasing about this way of creating music -- in fact, previous studies on other species of musical birds have failed to find evidence of this harmonic similarity to humans. Just because they follow our rules doesn't mean that hermit thrushes are doing so consciously, so we might not actually be singing the same tunes.