How important is social facilitation for dustbathing in laying hens?

Hens in a group usually synchronize dustbathing, such that when one hen starts to dustbathe she will often be joined by others. The sight of another hen dustbathing could thus possibly act as a stimulus increasing motivation for dustbathing, with important implications for hens in furnished cages, where the size of the dustbath normally allows only one hen to dustbathe at a time. If a hen is more motivated to dustbathe when she can see another hen dustbathing but she cannot get access to the litter since the dustbath is occupied, frustration may arise. The aim of this study was to investigate the effect of social stimuli on dustbathing motivation. Pairs of hens were exposed to one of three stimuli while being thwarted of dustbathing and they were thereafter given access to dustbathing material. The stimuli were (1) the sight of other hens dustbathing (DB-HEN), (2) the sight of a dustbath with other hens not dustbathing (NODB-HEN) and (3) the sight of a dustbath only (NO-HEN). Twelve pairs of hens were tested both deprived and non-deprived of litter in a balanced within-subject design. Irrespective of deprivation state, hens walked more and spent more time facing the stimulus in DB-HEN than in NO-HEN, and when they were not deprived they also walked more in DB-HEN than in NODB-HEN. Subsequent dustbathing behaviour when hens were given access to litter after the stimulus exposure was unaffected by the type of stimuli. We suggested that subtle effects of social stimuli on dustbathing motivation may have been masked by the effect of long litter deprivation and that it may be important for the birds to be able to join the stimulus birds to dustbathe together. For these reasons we repeated the experiment with individual hens and with a shorter litter deprivation time and a shorter stimulus exposure, after which the test hen was allowed to join the stimulus hen. Furthermore, in this second experiment hens were tested only in DB-HEN and NODB-HEN treatments. We found more displacement preening and less time facing the stimulus in DB-HEN than in NODB-HEN, but dustbathing behaviour was still unaffected by previous social stimuli. In summary, dustbathing behaviour of the test hens was not affected by seeing other hens dustbathing, but increased walking and displacement preening indicated a possible change in the motivation of test hens observing other dustbathing hens. [Copyright &y& Elsevier]