Cutaneous water evaporation—II. Survival of birds under extreme thermal stress

Abstract

1. 1. Two birds, the pigeon ( Columba livia) and the partridge ( Alectoris chukar), differing in their habits and flight ability were compared with regard to their ability to survive extreme high air temperatures ( T a s). During 270 min survival tests birds were exposed to T a's between 45 and 60°C and low relative humidities. 2. 2. The pigeon was observed to be unique in its ability to survive 270min of exposure to 60°C while regulating T b at 43.8°C. The partridge could not survive 270 min of exposure at T a's exceeding 48°C. 3. 3. The pigeons were found to be exceptional in their capacity for cutaneous evaporation. Values as high as 20.9mg H 2O/cm −2/hr were measured at 52°C T a compared to 2.4 mg H 2O/cm −2/hr in the partridge. Total evaporation of the pigeon exposed to 56°C T a was about 20% higher than that in the partridge. Maximum evaporation of the pigeon exposed to 60°C T a was 34.4 mg H 2O/g/hr. 4. 4. The significance of cutaneous water loss for survival during extreme high T a's is discussed. 5. 5. It is concluded that birds as a class may be divided into two groups with regard to their physiological capacity to withstand heat stress: (1) the majority of studied species employ regular physiological mechanisms and are limited in their cooling capacity to withstand ambient temperatures 48°C: (2) a few avian species, which may be of wide ecological distribution, are equipped with major physiological preadaptations to severe heat stress.