I read the first and last couple pages of the article. It starts to make my head hurt at some point, but I get the gist. I thought it was interesting that the feathers over their ears are designed to let sound through. And owls with asymmetrical ears tend to be better at hearing higher frequencies. Which seems to be because they have more space in their inner ear, and more tiny hairs that can amplify or transmit the sound.
The fish sounds were interesting too. It sounds kind of like the deeper sounds might be coming from the swim bladder. Off topic but fun fact: the swim bladder can change during the breeding season so it's easier to make mating calls for hours on end.
I love the first picture because it looks like the owl has flaps and spoilers. I didn't realize their feathers can ruffle up like that.