My ducks are three weeks old, rouens, and the brooder is getting a little crowded. Would it be okay to put them outside overnight? It's getting down to about 68-70F where I live. I only have one heat lamp so I wouldn't be able to give them one outside. I have a shelter where I can keep them out of the rain. They're getting kinda big and need more space but I don't want to hurt them. Thanks for any help.