Conjoint preferences of chicks for heat and light intensity

Small flocks of 400 chicks were kept in rooms with spatial gradients of light intensity and black bulb temperature. Their conjoint preferences for heat and light intensity were observed from 1 to 14 d of age. 2. High light intensities and temperatures were more attractive in combination than separately. 3. For chicks kept in an heterogeneous environment at an air temperature of 24°C, the ranges of light intensities and black bulb temperatures preferred by 90% of clustering birds were 1 to 21 lux and 24 to 32°C at 1 d of age. The upper limit of the preferred temperature fell to 27°C at 14 d of age, while the preferred light intensity remained the same. 4. Interchange of the light intensity distribution from homogeneous to heterogeneous and vice versa at 15 d of age and a uniform temperature distribution had no effect on growth rate or food intake but increased mortality. 5. The practical implication for poultry husbandry is that radiant heaters should incorporate an attraction light, or some other form of constraint, because chicks have some difficulty in locating sources of heat during the first few days of life.