Here in Western Pa, our weather can be quite irregular. Yesterday it was in the 50s, today its 22! Oh and it rained a bit last night before it got cold enough to snow. This is what greeted me this morning:
Those are ice coated feathers on their backs. I wasn't home to chase them in at dusk, I was working. It was too warm for them to want to go in themselves, so 6 of them slept in the trees. Luckily everyone made it through the night and had a warm breakfast and are now huddled in their draft-free coop warming up. Had I been home though, I would have certainly tried my hardest to get them in. Obviously they're not in any sort of distress about it.
Even though I learned as much as I could before I got them I still was not prepared for how cold tolerant they really are! They actually do better in cold temperatures then most chickens do. I still worry about them in freezing weather though so I do my best to take care of them and keep them inside on the coldest of nights.
Here's what I do:
First, I train them to come when call: I call "Guinea Guinea Guinea" whenever I throw scratch or treats. It doesn't matter what words or noise you use as long as you use the same thing every time. I start this when they're little, from the first time I give treats.
I train them to sleep in the coop: once they get big enough to free range they discover trees. What fun it is to fly way way up into the branches! To keep them sleeping in the coop and not the trees, right before dusk I call them and scatter treats right in the door way of the coop. I even toss a handful inside. Turn the light on if you have one. Most of the time they just hop up onto the perches after their snack. I hang out around the coop and try to shoo them back in if I can. They usually get the idea. A few weeks of this should be enough. The won't always want to go in to sleep, but they get that idea that they can and should
Keep an eye on the weather channel: If the weather is going to change drastically overnight, or if freezing rain is called for I chase them in at night. They're not very good at predicting weather, so I try to handle that for them.
Check them in the morning: I count every bird every night. I always know how many are out and how many are in, and which trees they are in. After a bad night I make sure everyone who spent the night outside gets a warm breakfast (warmed mash, the flavor of oatmeal no-one will eat, dinner leftovers, boiled rice and eggs etc) and get shooed into the coop to warm up.
Don't stress them: I pick up my chickens and dry them off, but Guineas aren't touchy-feely birds. They would rather I plug a heat lamp in for them and walk away then try to blow dry them in the house, which the chickens love! (always secure a heat lamp in 2 ways. I use the clamp and an additional hook)
Don't worry about their wattles: Chickens with large wattles tend to have a problem in winter because they dip into the water when the chicken leans his head down to get a drink. The water on the wattles then freezes causing frostbite. Guineas wattles are nowhere near as long or flexible. They stay in place so they don't fall forward and dip into the water. Also, that's not a comb on top of the guineas head. Combs are made of cartilage and the guineas horn is actually bone, so their is nothing to become frostbit.
When I first got Guineas it took me awhile to wrap my mind around them doing so well with the cold and snow. After all, they are originally from Africa so my brain just couldn't comprehend that idea at first. After raising them for 7 years I am completely confident that they can handle the cold and do so better then chickens.