Comb frostbite is always the biggest one for me, specifically with temperatures below -10F paired with humidity of about 98%. On those max humidity days, my nostrils start filling with ice as soon as I step outside. That's in the best ventillated environment (the outdoors) and in still air. For my flocks, a lot has ended up being down to the invidiaul bird and whether they are able to keep good circulation and therefore warmth in their comb, so thick combs do better than thin, etc. Birds that get purple tips in milder chilly weather are more likely to get toasted tips if they can't get the comb far enough into their feathers.
Sometimes water is another big one for me. I haven't had to worry about it for a while, but I was recently reminded of it because I had to take up a couple extension cords to let vehicles through the area for a few days in nasty temps. So much hauling water...since if you want it to stay thawed it has to be a pretty decent volume, and just breaking the ice on top only keeps the liquid accessible for a quick sip - it hardens up again quite fast if the water isn't warmer. I've got my heated bases plugged in again today and very much appreciate them.
Sometimes water is another big one for me. I haven't had to worry about it for a while, but I was recently reminded of it because I had to take up a couple extension cords to let vehicles through the area for a few days in nasty temps. So much hauling water...since if you want it to stay thawed it has to be a pretty decent volume, and just breaking the ice on top only keeps the liquid accessible for a quick sip - it hardens up again quite fast if the water isn't warmer. I've got my heated bases plugged in again today and very much appreciate them.