Yawning is a familiar and phylogenetically widespread phenomenon, but no consensus
exists regarding its functional significance. We tested the hypothesis that yawning
communicates to others a transition from a state of physiological and/or psychological
arousal (for example, due to action of a stressor) to a more relaxed state. This arousal
reduction hypothesis predicts little yawning during arousal and more yawning (above
baseline) during and after down-regulation of arousal. Experimental capture-restraint tests …

Liang et al.(2015) recently reported on the relationship between yawning and stress
responses in a wild population of Nazca boobies (Sula granti) in the Galapagos. Their
analysis covered two separate investigations: a human capture-restraint stressor applied to
adult boobies, and observations of nestlings maltreated by Non-parental Adult Visitors
(NAVs). The authors conclude that the temporal sequence of yawning following these
stressors provides support for the newly termed arousal reduction hypothesis, an idea …