Our first batch of chicks were in a cardboard brooder in the garage under a heat lamp, and I carefully monitored temperatures until they were about 2 weeks old. Then, one afternoon my dh wanted to give them some time outdoors during July when it was about 90 degrees F, so we set up a round of hardware cloth and they really seemed to like it! It was so much fun watching them jump around on the grass! Then, I left for a few hours to go shopping, and when I got back in the afternoon, they were all dead. The tree shade they had been set up under was gone by afternoon, and apparently the heat from full sun killed them. I put a thermometer on the ground there, and it read almost 110 degrees F. I hadn't realized how vulnerable they still were at 2 weeks to excessive heat. Heart breaker. We almost decided then and there not to have any more livestock, ever. But a second batch of day old chicks was ordered, and thankfully, the pullets are close to laying first eggs. But I'll never forgive myself that terrible mistake.