Cutaneous water evaporation--I. Its significance in heat-stressed birds.

In a comparative study on avian cutaneous evaporation, two species of Phasianidae, Japanese quail Coturnix coturnix japonica and chukar partridge Alectoris chukar, and three species of Columbidae, palm dove Streptopelia senegalensis, collared turtle dove Streptopelia decaocto and rock pigeon Columbia livia, were investigated. The skin resistance to vapor diffusion (rs) and cutaneous water loss (CWL) were studied in these birds exposed to air temperatures (Ta) between 20 and 52 degrees C. The skin resistance was measured with Lambda instrument diffusive resistance meter. Skin resistance within the thermo-neutral zone varied between a minimum of 62 sec/cm in the palm dove exposed to 20 degrees C and a maximum of 309.1 sec/cm in the partridge exposed to 36 degrees C. The CWL values were 2.5 mg H2O/cm2.hr and 0.51 mg H2O/cm2.hr respectively. Maximum CWL of the quail and partridge was 1.9-2.1 mg H2O/cm2.hr, equivalent to a cooling capacity of about 17% of metabolic heat production at 45 degrees C Ta. In the palm dove, collared dove and pigeon CWL reached 6.8, 13.1 and 20.9 mg H2O/cm2.hr and rs values reached 31.2, 16.2 and 9.4 sec/cm respectively. The cooling capacity amounted to 51.5, 86.1 and 96.5% of metabolic heat during heat stress (52 degrees C). The significance of skin evaporation in body temperature regulation of heat-stressed birds is discussed.