I've slept in a bothy while walking but not when I've been on the bike, what do you do with the bike over night?

In my (limited) experience - if the bothy is full leave it locked outside; if the bothy is empty, take it in; if the bothy is occupied but quiet ask if others mind you taking it inside (I've never known a refusal).

There is often a wood storage area that is covered that you can put your bike in if you can't bring it inside as psling says

psling wrote:In my (limited) experience - if the bothy is full leave it locked outside; if the bothy is empty, take it in; if the bothy is occupied but quiet ask if others mind you taking it inside (I've never known a refusal).

This, but I've never felt the need to lock it up on the few occasions it has stayed outside.
On the 2015 Scottish winter bivi at Bunnies bothy we all made the mistake of leaving them outside even though we could have brought them in. Result was everything froze solid, chains, brakes, gears, everything. Made for an interesting ride the first few hours.

I've always taken mine in, to be honest if there were a few people already there I'd go and sleep somewhere else unless I was desperate

Sign of a posh bothy is a bike shed (aka wood / tool store!) To be honest if the bothy is quite nice inside and my bike is filthy it stays outside and I've never felt the need to lock it. Exception is carnmore in Fisherfield as its got an earth floor.

Ray Young wrote:

psling wrote:In my (limited) experience - if the bothy is full leave it locked outside; if the bothy is empty, take it in; if the bothy is occupied but quiet ask if others mind you taking it inside (I've never known a refusal).

This, but I've never felt the need to lock it up on the few occasions it has stayed outside.
On the 2015 Scottish winter bivi at Bunnies bothy we all made the mistake of leaving them outside even though we could have brought them in. Result was everything froze solid, chains, brakes, gears, everything. Made for an interesting ride the first few hours.

Fond memories of my first proper bikepacking trip Ray, I was stuck in first gear for the first 5 miles

In fairness though, it was absolutely freezing that morning!