Poultry Overheating an Issue in Summer
Ashley Wright of University of Arizona Extension notes how to tell if a backyard chicken is in heat stress, and how to help to prevent potential heat stroke.
"monitor your birds and know the signs of a bird is going into heat stress. Birds that act normal are probably fine, but still need to be monitored. You may need to offer some cooling to them, but they are most likely fine. Be looking for birds that are not moving and are just kind of crouched with their wings out and panting heavily, those can be signs that the bird is in danger.
---For older birds, the risk of heat stress is greater because as birds get larger, they also become more insulated with their feathers.
To keep birds from overheating on hot days, the best thing you can do is make sure plenty of water is available... but you can also add electrolytes to the water. There are a number of homemade electrolyte solutions for chickens.
Overheating is a big problem in summer months for poultry farmers, because birds that are too hot will lay fewer eggs and hatchability, egg shell quality, internal egg quality and egg size may all decrease.