On a hot summer day I watched a group of ravens sunbathing. They had gathered on a lawn next to a white shed, a bright and hot spot sheltered from the wind where the sun's rays were amplified. Some of the big black birds had their wings half-spread, like a droopy cape, and all had their mouths open. They looked like dogs panting, although they did not have their tongues hanging out. It was an odd picture - they seemed uncomfortably warm, but they had clearly sought out this hot spot.
Birds don't sweat. Their primary means of cooling is through their lungs. Fresh air coursing thru their respiratory system picks up internal body heat and warm moist air is exhaled. Those ravens I saw really were panting - increasing the flow of air over the moist surfaces of the mouth and bronchial areas. Ravens also thermoregulate by spreading their wings to dissipate heat, as I saw; and by flying to cooler air layers and soaring in the cool air.
Ravens' normal body temperature is about 103 degrees, a bit higher than humans' 98.6. Our temperature doesn't fluctuate much under normal conditions, but birds' temperature normally fluctuates a few degrees depending on outside temperature, metabolic activity such as digestion and activity - a flying bird produces about nine times more heat than a resting bird.
Why the ravens I saw were deliberately basking in the hot sun is a mystery, but people do the same thing.