When I get my 6-8 week old light sussex.......will they be feathered out enough to NOT need a heat lamp in the coop? Is it their 'age' or degree of 'feather-out-ness' that will determine whether or not they need supplemental heat? What night time temp. range should be okay for them at that age? 40 degrees? 30 degrees? or will they still need a heat lamp over an area in the coop to bring the temp (under lamp) up to what temp? How do I tell?