I have been checking my four chickens every few days for mites, since two of them have been losing feathers. Thankfully it just seems to be a mini molt. However, tonight I noticed one of them had a black mark on her foot, and at first thought it was just mud. It has been raining and snowing a LOT lately. It didn't come off. My daughter and I brought her in and gave her feet a bath in room temp water, and I am wondering if it is frostbite. I feel awful, because I hadn't noticed earlier. It has been so muddy for weeks, so their feet are always dirty. Pics below. It hasn't been that cold...the coldest has been 25 degrees a few nights ago, but with all the wet weather, I guess it could happen. We brought them all in and cleaned them up, and she is the only one affected. The coop has enough ventilation, but it has been impossibly rainy/snowy lately. The ground has been mucky for weeks now. Since they are all wet tonight, they are sleeping in the guest bathroom tub tonight, on a blanket. There was a black spot on the bottom of each foot as well. One turned out to be a clump of dirt. I didn't rub the other one in case it was frostbite or bumblefoot, as it didn't come off easily. She is walking fine and not favoring the foot. Sorry the picture quality isn't good...she doesn't like to be held down and I couldn't get it to focus up close. I will try to get a better picture of the bottom of the foot tomorrow.