J.W.E Stam, Pigeon Racing Today & Tomorrow, dedicates an entire chapter on pigeon transportation. He calculates transport temperature, available oxygen, relative humidity, and carbon dioxide within the transport based on air exchange, size, and number of birds being transported. Valuable information for transports parked during hold overs.
"The highest temperature at which a pigeon can remain comfortable is 105 degree Fahrenheit. Above this point it will have great difficulty in regulating its body temperature and will quickly die of hyperthermia. The lowest temperature which a bird can withstand is probably around minus 5 degree Fahrenheit."