My 12 chicks are very rapidly outgrowing their brooder! They are 8 weeks old and fully feathered. Temps here in central OK are ranging anywhere between 60 and 75 during the day and 40 and 50 at night. Can i move them outside without a heat lamp? They have a draft free coop and enclosed run. No other chickens to worry about. Their brooder (2 of the next to largest size available rubbermaid tubs joined together) is too big to move back and forth.