Experimental Evidence of Contagious Stretching and Ingroup Bias in Budgerigars (Melopsittacus undulatus)

Previous observational research suggests that stretching is contagious in budgerigars (Melopsittacus undulatus). Here we report the first experimental evidence of this response through a reanalysis of a previous experiment testing for contagious yawning in this species. Using a repeated measures design, 16 birds were tested as pairs alongside familiar and unfamiliar conspecifics with and without visual barriers. Our results show that stretching behavior was temporally clustered only when the birds could see one another, corroborating previous observational findings supporting contagion. Additionally, for the first time, we show an ingroup bias in this response. That is, while the overall frequency of stretching did not significantly differ as a function of conspecific familiarity, contagious stretching was only present when cage mates were paired together. These findings are discussed in relation to recent research studying social cognition in this species.