Because evaporative cooling is the principal avenue of heat loss at high ambient temperatures, high humidity superimposed on high temperature presents poultry with an additional thermal challenge. Whenever body temperature exceeds ambient temperature, sensible heat loss (radiation, conduction, and convection) to the environment will occur. The generally accepted model of heat balance, which states that when ambient temperature increases homeotherms will endeavour to maximize sensible heat loss before resorting to evaporative heat loss, was recently challenged. However, several factors that can influence heat balance were not considered in the reasoning pursued in that challenge. In this paper the theory behind heat balance models is discussed and the data that were used to challenge the model are reanalysed. The question of whether poultry are capable of physiologically increasing sensible heat loss under hot, humid conditions remains unanswered and presents an area worthy of future study.

Models of heat loss partition in poultry suggest that, above the zone of thermoneutrality, insensible heat loss increases while sensible heat loss mechanisms decline in importance. Comparison of evaporative and total heat losses at low and high relative humidities suggest this may not be correct at high temperatures and high humidities.