Demand for nest boxes in laying hens

Domestic hens (Gallus gallus domesticus) from commercial laying strains have been selected for high egg yield and may lay over 300 eggs in their working lives. In conventional wire cages, there is little opportunity to perform either nest seeking or nest building activities, which may lead to frustration each time an egg is laid. To measure the demand for a well-defined nest-site, which may act as a consummatory stimulus for nest seeking behaviour and an appetitive stimulus for nest building behaviour, 16 hens were allowed to work to gain access to a pen containing two littered, enclosed nest boxes. The cost of access to the nest boxes was varied by changing the width of the vertical gap, which divided a home pen containing food, water and a perch from the pen containing the nest boxes (gaps of 220, 140, 125, 110 and 95 mm, compared with mean body width of 117 mm). The number of entries to the nest pen declined with narrowing gap, whilst the number of failed attempts to enter rose, but all 16 hens persevered with entering the nest pen prior to oviposition and laid in the nest boxes. Between 120 and 30 min to oviposition hens made many entries with the 220 mm gap (27.6), but this declined to no entries with 95 mm gap. Hens made few entries in the last half hour prior to ovipositoin (1.3) but there was no significant decline in entries as the gap narrowed (1.1 with 95 mm gap). The number of nest inspections and nest entries also declined with width of gap, but there was no effect on time spent in the nest boxes. Hens passed gaps of 220, and 140 mm to return to the nest pen following oviposition, but did not pass gaps of 125, 110 or 95 mm. We therefore conclude that the narrow gap width can be used to assess the demand for environmental requirements. Hens were willing to pay a high cost to gain access to a nest box prior to oviposition, so prelaying behaviour may be frustrated in hens without a well-defined, littered nest site.