The logic behind the little birds: they are DIVs with CSS animated on a cubic path up-and-down, while their ::after is getting animated on a different cubic path left-to-right. The result of 2 separate axis animations: They do a loose figure-8 path that's different each pass.
That CSS code is here: https://github.com/simonsarris/site-simonsarris/blob/master/...
I am currently trying to make my site background considerably more ridiculous by re-implementing in canvas, with lots of interaction and a night/day sequence, and custom buildings. The rebuild so far is open source here: https://simonsarris.github.io/simeville/
Click the button to build a town. Drag the sun down to see night time (and the constellations). I need to spend a lot of time working on the art, but I'm not a very good artist yet.