Abstract

Twelve Isa Brown hens (Gallus gallus domesticus) were trained to open a locked door for access to a pen containing an enclosed nest box ('nest test') and to return to a home pen containing food, water, litter and a perch ('home test'). The door was connected to a computer-controlled load cell, which recorded work exerted on the door and unlocked the door when the hen had exceeded a predetermined workload. Following training, the workload was set at 10 Ns, and hens received one nest test per day at 80, 60, 40 or 20 min prior to oviposition, and then one home test per day after 1, 2, 3 or 4 h confinement in the nest pen. As oviposition approached, hens showed a higher work-rate for access to the nest pen, showed a shorter latency to use the nest box and spent a greater proportion of their visit time in the nest box. Hens also worked harder for the home pen, showed a lower latency to feed and spent more time feeding after their return as period of confinement increased. The hens' work-rate for the nest pen at 40 min prior to oviposition was comparable with their work-rate for the home pen after 4 h confinement, while their work-rate was at its highest in nest tests at 20 min prior to oviposition. The technique appears to be a valid means of assessing the importance of environmental resources, the values of which vary with time. The results suggest that hens place a higher value on gaining access to a discrete nest-site prior to oviposition than they do on gaining access to food following 4 h food deprivation.