Well of course you can... Just realize the risk (how secure your coop truly is will determine minimal risk vs average risk) involved in potentially losing one or more of your birds. My run is pretty daggone secure (although I still have measures to take), but it's not worth the risk to me. If I HAD to go a night or two without shutting it, I'd feel fairly confident that they'd be safe. But I would not feel confident about it becoming a regular thing on a nightly basis.