Mystery Solved!

Yep, after being nearly convinced I was listening to the nighttime serenade of a sea lion, I have figured out the mystery middle-of-the-night noise is actually some roosting double-crested cormorants!

Last night I went to investigate the sound closer, and it still very much sounded like it was coming from above. I shone a flashlight into the trees and the sounds stopped, and then I heard (but was unable to see) the ruffling of wings as a bird repositioned high up in the tree. So, I was back towards thinking the culprit was a bird, but nothing was confirmed until this afternoon at dusk.

I was out on the deck (sweeping up empty bird seed husks no less) when I noticed a lot of cormorants flying around. Huh, that's odd.....and look, one just landed up in those trees! This must be a new roosting spot for them as they haven't been around before this week. I went closer to investigate, with camera in hand, and was satisfied beyond a shadow of a doubt when one looked down at me with some of those eerie, gurgly, throaty barks.

(Also, credit where credit is due: the only person who made a correct guess as to what it might be is my mom!)