mine are bantams and i have them outside today with no heat lamp but its 79 here although it feels hotter. the other 2 days they have been outside i had a heat lamp on them and it was in the 60's and i even left them out till it got dark and dropped to the 50's, again they had a heat lamp so they stayed warm. i bring them in each night but i wont let them stay ouside without a heat lamp when its low 70's (73) or colder. they were hatched on nov 8th so they are about 5 weeks and a few days if my calculations are correct. they wont be going into the flock until they around 5-6 months old.