Chickens will use a number of strategies to regulate their body temperature.
They often pant if affected by heat stress, which increases evaporation from the lungs and lowers body temperature, they also use their feathers as an insulating mechanism to maintain their body at a constant temperature and to radiate heat away from the body.
Chickens will drink more water if they are exposed to higher temperatures in attempt to lower their body temperature. The internal body temperature can be measured with a normal thermometer that is inserted into the cloaca.
This can be done once the chicken is properly restrained (see “Safe and Humane Handling”). While holding the chicken, move the feathers to expose the vent. Gently insert the thermometer into the cloaca and wait until you get a reading on the thermometer.
A healthy body temperature will be around 40.6–43.0°C.