I have my recent batch of 3 barred rock girls and 3 silver laced Wyandotte girls I purchased at the same time. They were the same size upon purchase and up until recently have been as well. My Wyandottes are quite smaller than the Rocks for some reason. Anyway, I have had the girls inside in their brooder until yesterday. We had my daughter's second birthday party and I put them in the garage (heat lamp off) temps around 85 with the garage door open to let a breeze in. I went in there this morning to bring them back inside, and one of my Wyandottes was lying there dead, everyone else was fine. Anyone have any ideas what could've happened?