Muscovies are really hardy ducks, but as kuntrygirl asked it really depends on how cold you mean. They are originally from South America so they evolved to live in hot, humid climates but do so well in others that they are now considered a feral/invasive pest. They do well where I am which is the Los Angeles desert. We have hot, dry summers that hit about 100 degrees or more and the past two winters have been very rainy and very cold (for us, anyway lol) that got down to about 30 degrees or lower at night.