I’m presuming they are outdoor buns? Or indoor and outdoor ?

If 100% outdoor, the most important thing is that they have complete shelter from rain, wind and snow and all elements (and of course direct sun in summer). buns are more likely to die of overheating than from the cold.

50s which is 10°C is fine, that’s not cold at all for a bun who has a winter coat on. Straw is of course the ideal thing so they have the choice of burying down and keeping warm. The softness of the straw (if they’re not used to it) may make it into a toilet area though… so keep an eye on that.

If buns come indoors too, they can handle a temp change of +/-10°C so do respect that.

If it’s much colder outdoors, then its best to keep them out than bring them in to a hot centrally heated house and then back out into the cold within a short time.

Hope that helps

The only thing I can add is that the outdoors living area should either be elevated off the ground or have a “hidey-house” that’s elevated off the ground. That’s so cold won’t penetrate from beneath (air is an insulator). I don’t suppose it ever freezes in California but if it does, you need to give the rabbits warmed water twice a day (because they can’t drink frozen water – kind of obvious, but still sth to keep in mind.)

A little bit extra food can be required, keeping warm costs energy, growing extra fur costs protein.

So, now I added 3 things when I said I was going to add one