Maximum limit of sensible heat dissipation in Japanese quail.

Surface temperature can be used as a tool for calculating sensible heat transfer. However, it needs to be associated with air temperature to identify the direction of heat flow (gain or loss). This study quantified sensible heat transfer in Japanese quail as a function of operative temperature. The meteorological variables were air temperature, relative humidity, and black globe temperature. Quail surface temperature was measured on 50 adult Coturnix coturnix japonica individuals 270 days old during 8 days by using a thermographic camera. The data were analyzed by the least-squares method to assess the effects of sex (male and female), period of the day (morning and afternoon), and body region (head, body, and feet). Quail surface temperature was strongly correlated with operative temperature. The total sensible heat flow was 64.02 W m−2. The morning period had a mean operative temperature of 22.48 °C, providing a higher gradient between air and quail temperature and thereby producing a higher heat flow (82.19 W m−2). In the afternoon, the heat transfer was lower (45.70 W m−2) because the operative temperature was higher (30.84 °C). Comparison between sexes showed that heat transfer was higher in females (67.37 W m−2) than in males (60.53 W m−2). The head served as an important thermal window, with a heat transfer of 78.24 W m−2, whereas the body and feet had a transfer of 56.80 W m−2. Heat transfer by sensible mechanisms was quantified in Japanese quail. Heat transfer depended greatly on ambient temperature. When the operative temperature was below 28 °C, sensible mechanisms were efficient in dissipating heat to the environment. When the ambient temperature exceeded 29 °C, quail could not effectively dissipate heat to the environment through sensible mechanisms. At 30 °C and above, heat loss shifted to heat gain, causing thermal stress in Japanese quail. [ABSTRACT FROM AUTHOR]