Measuring the Strength of Social Bonds: Experiments With Hand-Reared Goslings (Anser Indicus)

Abstract

AbstractAllogrooming, dueting and other behaviours observed only between pair or group members are often said to reinforce or strengthen social bonds, yet the strength of these bonds was not measured independently. 'Bond strength' should reflect the stability of an attachment relationship and thus the probability of a permanent separation from the partner. The latter is a function of opportunity or external force as well as of an internal 'divorce tendency'. Only the divorcc tendency is inversely related to that motivational variable which can be called 'bond strength'. To find a behavioural measure of individual divorce tendency, the relationship of hand-reared bar-headed goslings (Anser indicus) to their human foster parents was investigated in four experiments. The following results were obtained: (1) The subjects (n = 18) significantly preferred their own, familiar foster parent (Hp) to a less familiar person (Hu). (2) This was also true when the Hu was the preferred Hp of another group of goslings, indicating that familiarity and not his suitability as a 'goose parent' is the relevant factor. (3) Alone with one person on a lawn, all goslings (n = 12) also maintained proximity when this was an Hu, indicating a bond to him also. Median distances maintained to Hp and Hu did not differ significantly, and were therefore no indicators of a gosling's preference. But the distress calling rate was significantly higher and the feeding rate significantly lower when a gosling was with an Hu than when with its Hp. (4) Distress calling rate in the presence of a stationary person was also a good indicator of a gosling's (n = 15) tendency to leave him and follow a slowly moving stranger. Approaches towards the stranger were significantly longer when the stationary person was an Hu than when it was the Hp. The amount of distress calling in the presence of an Hu was positively correlated (p<0.01) with the distance that the subjects later moved towards the stranger. The distress calling rate therefore is a good relative measure of a gosling's tendency to abandon a particular object, this tendency reflecting what we may call the strength of a bond or attachment.