The Social Facilitation of Drinking: What is Facilitated, and Who is Affected?

The effect of a drinking companion on conspecifics was investigated using domestic hens ( Callus gallus domesticus ). The two aims of the investigation were firstly to see whether drinking is sensitive to social facilitation, and if so, to see whether it follows the same pattern as that of feeding, i.e. whether it acts primarily on the drinking behaviour rather than the amount ingested. The second aim was to see whether differences in how influenced the birds were by a drinking companion correlated with one or more social or non‐social traits. Social facilitation was measured by comparing the intake and number of ‘head‐ups’ (i.e. swallowing) of an individual in the presence of a thirsty or non‐thirsty companion. The traits measured were as follows: the rank within each pair, social dependence/fear, reaction to a novel object, reaction in a feeding‐inhibition test, and finally weight (as a possible index of the overall rank of the birds in the group). Social facilitation of drinking occurs but acts primarily on drinking behaviour (number of ‘head ups’); birds do not swallow as much per ‘head up’ as when they themselves are thirsty. The lightest (possibly most subdominant) birds were also the ones most influenced by the drinking conspecific. Furthermore, the heaviest (possibly most dominant) individuals were the ones with the shortest social distance and the longest latency in approaching a novel object. This meant that the birds that were most influenced by a drinking companion were also the individuals that were least fearful and showed the highest degree of exploration.