Yawning is a rather complex reflex. It’s triggered under a variety of contexts and neurophysiological changes. It primarily occurs during periods of state change, commonly following transitions of sleeping and waking. There’s research that also suggests that yawns are initiated alongside increases in cortical arousal, so yawns themselves may function to promote alertness. And there’s a growing body of research that suggests that yawning is triggered by rises in brain temperature. I’ve conducted a number of studies testing this in humans, nonhuman mammals, and even birds.
https://www.science.org/content/article/why-yawns-are-contagious-all-kinds-animals https://open.spotify.com/episode/4sbxMHgUZ717pURQ6rosFh