The preferences of broiler and layer strains of fowl for four different intensities of incandescent luminaire (6, 20, 60 and 200 lux; Osram, 60W, pearl) were tested at 2 and 6 weeks of age. With each strain, four replicates of 12 birds were each allowed to move freely between four compartments illuminated continuously at the different intensities for 6 days. The distribution of light intensities among the compartments was changed daily. After 2 days of conditioning, the birds’ location and behaviour were recorded once every 15min over 23h on each of the remaining 4 days. The other hour was devoted to changing light intensities and refilling the feeders and drinkers. Six, mutually exclusive behaviours were defined: resting, perching, feeding, drinking, litter-directed activity and locomotion.

With both strains, most time was spent in the brightest (200 lux) environment at 2 weeks of age. but in the dimmest (6 lux) at 6 weeks. This apparent change in preference was associated only with the two behaviours which took up most time, resting and perching, whereas the highest intensity was consistently preferred for all other behaviours. Older birds thus preferred to be in dim light when they were relatively inactive.

The finding that older birds prefer to spend much of their time in a light environment of < 10 lux intensity, depending on behaviour, is contrary to current recommendations that minimum light intensities for broilers and laying hens should be increased to as much as 20 lux. Some variation in the spatial or temporal distribution of ambient light intensity, to provide both dimly (< 10 lux) and brightly (eg > 50 lux) lit environments, might benefit the welfare of older poultry, although further work is needed to establish their optimal light environment.

The illuminance and spectral power distribution in 19 duckling and 16 turkey poult houses in the UK were sampled. Illuminance was highly variable within duckling houses and to a lesser extent in housing for turkey poults. In a free choice experiment, the preferences of commercial ducklings and turkey poults for four incandescent illuminances (<I, 6, 20 and 200 Ix; Osram, 60 W, Pearl) were tested at 2 and 6 weeks of age. Four replicate flocks of 12 birds were given continuous access to four compartments illuminated with each illuminance for six days. The illuminances were changed daily between the compartments. After two days of conditioning, the birds’ location and behaviour was recorded at 10 min intervals over 22 h. Nine and 12 defined behavioural categories were recorded for the ducklings and poults respectively. Ducklings spent significantly more time occupying the three brightest light environments both at 2 and 6 weeks of age, and the least time in the dimmest. Illuminance had a significant effect on the partition of behaviours amongst the light environments. At 2 weeks of age, locomotion and environmentally directed pecking occurred most often in 6, 20 and 200 lx, whereas at 6 weeks, preening and feeding also occurred more often in these light environments. At 6 weeks of age, resting, standing and drinking occurred significantly more often in 6 lx than in the dimmest environment. Turkeys spent most time in the brightest environment at 2 weeks of age, but in 20 and 200 Ix at 6 weeks. This change in overall preference was reflected in the partition of different behaviours between the light environments. At 2 weeks of age, all behaviours were observed to occur most often in 200 lx. At 6 weeks, resting and perching were observed least often in <I lx, whereas all other activities were observed more in the two brightest light environments. These results show that ducklings and turkey poults have significant but differing preferences for illuminance, and imply that some spatial or temporal variation in the ambient illuminance of housing would be consistent with their preferences.