All my questions are valid questions and worthy of asking in light of the death of a group of chicks. The amount of feathering would have given some bearing on the age of the chicks, also a bearing on how much heat they would have needed, and any one using a heat lamp should be aware of how much heat that lamp was putting out in a brooder. To not acknowledge the bearing of these issues on this situation is to not be looking at the whole picture. And how would you know that they died from stress without looking at the whole picture? I am a fan of PND, and use it with all chicks. But PND will not solve brooder error.