Yawning and thermoregulation in budgerigars, Melopsittacus undulatus

Yawning is a widespread behavioural response expressed in all classes of vertebrates. There is, however, little agreement on its biological significance. One current hypothesis states that yawning serves as a thermoregulatory mechanism that occurs in response to increases in brain and/or body temperature. The brain-cooling hypothesis further stipulates that, as ambient temperature increases and approaches (but does not exceed) body temperature, yawning should increase as a consequence. We tested this hypothesis in a sample of 20 budgerigars, Melopsittacus undulatus, through the manipulation of room temperature. Birds were exposed to three separate conditions (control temperature (22 °C), increasing temperature (22–34 °C), and high temperature (34–38 °C)) in a repeated measures design, with each condition lasting 21 min. The incidence of yawning differed significantly across conditions (4.20 ± 2.39 yawns per bird in the increasing temperature condition, compared to 2.05 ± 1.90 and 1.25 ± 0.72 yawns per bird, in the high temperature and control conditions, respectively). These findings are consistent with the hypothesis that yawning serves a thermoregulatory function.