I'm getting very concerned. We bought 6 leghorn chicks in April. In August we started getting eggs. We were typically getting 5 eggs a day. All the girls have done very well in what was a very hot summer and now that the temps have cooled. Over the past 3 weeks I have lost 3 chickens. Each seems fine only to be found dead later in the day. We have not observed any symptoms of flu. I am at a loss to figure out the cause. All have looked healthy. Been eating and drinking normally. Ideas?