My Muscovy duckies are free range during the day. At night, ever since they have been outside, I put them up in a triangular prism shaped tractor. The last three days, they have been very resistant to going up at night -- they just want to sleep in a bunch on the ground. They are 3 months old. Is it safe to let them stay out, or should I keep struggling with them to get them to go up? During the day they sometimes will go in the tractor to lounge -- it has shade and is waterproof, although they like to be out in the rain sometimes, too...so I don't think it's just because they don't like the tractor. Suggestions, anyone?