Thanks to all for the well-wishes. We do get quite attached to our animals, and we try to take very good care of them. So it is a blow on two levels - 1 We get attached to them and 2 we wonder what did we do wrong.
My initial thought was illness of some sort, but it seems odd that an illness would kill them all at once, and that there are no other symptoms that I am aware of. They have been active and eating and drinking normally, and their stool is not oddly colored or bloodied.
I also thought of some sort of toxicity, but could not think of what may have caused it.
We used the same food product, same water, and same bedding as last year. The only thing we did differently this year was we purchased a metal bin such as the farm store keeps their chicks in.
Temperature in the tub was about 98 degrees directly under the heat lamp.
As for the heat lamp vapor theory, that makes sense, and I had never heard that those bulbs released anything toxic, so I'm glad to know it for the future. But that bulb had heated them for four days, and was much closer to them to keep the temperature up in the first few days. At the point they died, the bulb was suspended some two feet above the base of the tub, and above the top edge of the tub. The fumes then would not be trapped in the tub, but exposed to the air flow in the house. Perhaps I'm overthinking that, though.
We've checked this site to learn a great deal in our Chicken keeping in the past, so we knew this would be the place to come for this problem! Thanks for all the suggestions.
