There is a slider in the settings that just lets you choose between "bird" and "worm" values.
Has anybody found out what this is for?
I've managed to get no clue about it yet...

I don't know either. I'll be back when I figure it out but I think it has something to do with the saying "The early bird gets the worm." With how cryptic the writing in this game is I doubt it will be that easy though. It can be anything. Perhaps we need to level up our Aspect: Cultist Simulator Lore to be able to understand that. ;)

If my occult sources (reddit) are correct it's part of an ARG that also involves the Fallen London website. So, as far as any effects on the game itself are concerned, it probably doesn't do all that much...

Try looking for the bird in a "safe" place ;)

I still haven't found the answer, but luckily I found this instead :)