Handling stress initially inhibits, but then potentiates yawning in budgerigars (Melopsittacus undulatus)

In mammals, yawning is associated with social and physiological stress, as well as thermoregulation, but little is known about why yawning occurs in stressful contexts or how it is integrated with natural stressors. To investigate the stress sensitivity of yawning in birds, we exposed budgerigars (Melopsittacus undulatus) to a handling stressor that simulated a predatory encounter. Each bird was captured, gently held for 4 min, and then released and videotaped for 1 h (experimental). On a separate day (±24 h), the undisturbed animal was videotaped for 1 h (control). The relationship between handling-induced yawning and body temperature was assessed in a separate experiment, in which the underwing temperatures of the same birds were measured at 1 min intervals during a 4 min holding period. After handling stress, yawning frequency was initially suppressed, then sharply increased within 20 min. Underwing temperature increased during handling, and individuals’ final temperatures at minute 4 were negatively correlated with their latencies to yawn after handling. Thus, stress-induced hyperthermia may be responsible for associations between yawns and stress. These results indicate that yawning may offer a sensitive, noninvasive measure of stress in birds.