Two weeks ago, I moved 4, 10-day old chicks to an outdoor brooder with an attached run. For the first couple of days I, had a heat lamp on them, but then summer hit. It was over 90 degrees and so hot I turned off the lamp and opened the door to the run, so they could get out into the fresh air. They loved their new freedom. The first night I put the heat lamp back on, as temps were supposed to drop below 70. By the next night, however, it was still around 80 degree when we went to bed, the chicks seemed in no distress, so we left it off. It hasn't been on since and the chicks are now 3 weeks old -- with wing and most of their back feathers, but they still have fuzzy heads, butts and bellies. It's been getting progressively cooler at night. Last night the low was 62, but when I checked them in the morning they looked fine and lively. Now we are going to see nighttime lows in the high to mid-50s and I'm wondering if I should get the heat lamp back on. I did make a little cubby-hole in their brooder they could sleep in to preserve body heat, but don't know if they will use it. I hate the fire-hazard aspect of a heat lamp and so far it appears to have been totally unnecessary. At three weeks they seem surprisingly hardy, but I don't want to push it.