The body temperature of birds has more variability than mammals. The normal temperature of an adult chicken ranges between 105°F and 107°F, whereas the one of a hatchling is lower. Smaller breeds have a higher temperature than larger breeds. Activity also increases body temperature. A body temperature above 115°F or below 73°F is fatal. A chicken who doesn't eat for just one day drops about 2.5°F in temperature, and one who doesn't eat for a second day drops another degree.