TABLE 1.

Overview of heat stress effects on chicken behavior.

Class	Heat stress effect	Pros	Cons	References a
Behavior	↑ respiratory rate (thermal polypnea or panting) → thermal hyperpnea	↑ latent heat dissipation (evaporative heat loss through the respiratory tract)	Dehydration → higher water requirement and consumption	Richards (1970) , Jukes (1971) , Brackenbury and Avery (1980) , Dale and Fuller (1980) , Teeter et al. (1985) , Odom et al. (1986) , Marder and Arad (1989) , Yahav et al. (2004) , Borges et al. (2007) , Renaudeau et al. (2012), Rhoads et al. (2013), Wang W. C. et al. (2018) , Beckford et al. (2020) , Wasti et al. (2020)
			↑ CO2 loss → hypocapnia → respiratory alkalosis (acid-base imbalance) → ↓ blood calcium for eggshell mineralization and ↓ growth performance
			↑ energy expenditure to maintain euthermia → ↓ performance
	Wing lifting	↑ exposition of unfeathered body surfaces → ↑ sensible heat loss	↑ energy expenditure to maintain euthermia → ↓ performance	Dale and Fuller (1980) , Baumgard and Rhoads (2013), Wang W. C. et al. (2018)
	Lethargy → ↓ feeding and walking	↓ metabolic heat from digestion, absorption, and nutrient utilization	↓ performance	Dale and Fuller (1980) , Teeter et al. (1985) , Geraert et al. (1996a) , Baumgard and Rhoads (2013), Hester et al. (2013) , Wang W. C. et al. (2018)
			↓ bone/skeletal health

Upward arrow (↑), increase; downward arrow (↓), decrease; rightward arrow (→), consequence/degeneration.

^aInclude studies on non-avian species that have exhibited comparable heat stress effects and responses to those observed in chickens. Studies with the focus on chickens or poultry are highlighted in bold.