An evaluation of heat exchange in small birds

Summary Equations are derived that quantify the component thermal resistances to heat transfer in small birds and account explicity for the effects of variation in these resistances. Heat transfer theory is used to quantify external resistances, and an experiment was conducted to estimate body resistance (r _b, plumage plus tissues) as a function of external temperature and wind speed. The value ofr _b decreased with wind speed, and decreased as air temperature approached 0°C. Heat transfer from small birds is shown to be relatively independent of external resistances and mainly dependent onr _b. The predictions of the new theoretical equations are shown to agree well with existing empirical data.