Normally, the chicken's body temperature is 104-107 o F, but will fluctuate somewhat depending upon the temperature of its environment. However, there is much less flexibility on the high side. The chicken must be able to get rid of excess body heat quickly or it is in trouble. Although birds and mammals are homeothermic, birds have a number of thermoregulation characteristics different from mammals. The most obvious is feathers.
Feathers are great insulation which is good for cold weather but bad for hot weather.
Feathers tend to hold heat in and not let it escape easily from the chicken's body. Another difference is that birds have no sweat glands. Most mammals perspire when they are hot, and evaporation of this perspiration from their skin is extremely effective in reducing body temperature. Nevertheless, birds have a couple of special features that do help them during hot weather. Their relatively high body temperature makes it easier for them to lose heat to the air around them.