I've always heard that they can take the low temperatures, but the cold wind can hurt them if those temps are really low. I've always used the windchill factor to decide whether or not I'll shoo the birds into their barns. Because I'm overprotective, that number is 20 degrees. For example, the temp right now is 18 and winds are 15-25mph. That's a lot of wind for this area. This makes temps feel like 5 degrees, so the birds went in their barns. The cool part is that they don't like the wind, so now they usually go inside on their own. Visualize a short, middle-aged lady in coveralls herding peafowl. That would be me. (You're laughing, right?) This is not a pleasant sight, so I'm very happy that my birds finally "get it" that the barn is a very comfortable place to be on cold and windy nights. They have started heading in without my "encouragement".
My oldest male, an IB who is about 20, came to me with a couple of missing toenails. Because the tips of those toes are an unusual color, it's possible he lost the toenails to frostbite.