MOTIVATIONAL ASPECTS OF INDIVIDUAL VARIATION IN RESPONSE TO NESTBOXESBY LAYING HENS

Laying hens, Gallus gallus domesticus, show individual Variation in pr e-laying behaviour including their ultimate choice of nest site. In ho using systems with nestboxes, the majority of hens make a small number of long visits to nestboxes and lay their eggs therein, but some hens make many short visits and occasionally lay outside the nestbox. We i nvestigated the motivational basis of this individual variation using six consistent hens which always laid in nestboxes and six inconsisten t hens which sometimes laid outside nestboxes. Each hen was housed in a pen (containing either no nestbox, a semi-enclosed nestbox or an enc losed nestbox) with access to a ring-shaped tunnel which increased the opportunity to perform locomotor activity. Access to the tunnel could be restricted by narrowing the doorway to 140, 125, 110 or 95 mm (com pared with a mean hen width of 114 mm). In trials with no nestbox, the re was no difference in the pre-laying behaviour of consistent and inc onsistent hens. Narrowing the doorway reduced the number of visits to the tunnel, but all hens persisted in visiting the tunnel and doorwidt h had no effect on time spent therein. With both designs of nestbox, h owever, inconsistent hens visited the tunnel more often than consisten t hens prior to oviposition, and continued to pass the narrowest doors to enter the tunnel, whilst consistent hens would not pass doors of 1 10 or 95 mm. After oviposition, there was no difference in the two gro ups' behaviour in any treatment and no hens would pass doors of either 110 or 95 mm to visit the tunnel. Individual variation in nest-site c hoice, therefore, appeared to result from different perception of nest boxes rather than lower nesting motivation. Inconsistent hens worked a s hard as consistent hens to perform pre-laying locomotion, but appear ed to be less responsive to the cues provided by nestboxes than consis tent hens, because they persisted with pre-laying locomotion when prov ided with either design of nestbox. (C) 1997 The Association for the S tudy of Animal Behaviour.