Every photographer is thrilled when a lion yawns. The wide-open mouth, with its bared teeth and protruding tongue, makes for a fantastic subject. But has anyone ever wondered what triggers a yawn and what purpose it serves?
Yes, researchers have indeed investigated this. And the organisation Wildlife Vets Namibia addressed this in their latest newsletter. Before discussing cause and function, however, let's first define what we mean by yawning.
"A yawn is a reflex in vertebrate animals characterized by a long inspiratory phase with gradual mouth gaping, followed by a brief climax (or acme) with muscle stretching, and a rapid expiratory phase with muscle relaxation, which typically lasts a few seconds", Wikipedia states.
Adding: "Almost all vertebrate animals, including mammals, birds, reptiles, amphibians, and even fish, experience yawning." – Now to the question of what happens when you yawn.
Many believe that deep, long breaths increase the amount of oxygen in the blood, needed by the brain. However, as Wildlife Vets Namibia and Wikipedia point out, several studies have failed to confirm this.
A better-supported explanation is that yawning helps cool the brain. Deep breathing and stretching facial muscles allow more cool blood to flow to the brain.
This is also supported by an observation from researchers mentioned by Wildlife Vets Namibia: larger animals with more brain mass tend to yawn longer. The larger the brain, the more cooling it requires.
Spontaneous and contagious yawning
Preparing to rest: Yawning lioness in Etosha National Park in northern Namibia. Photo: Sven-Eric Stender
But now back to the original questions about the triggers and functions of yawning. We humans yawn when we are tired or bored, but also when we wake up.
And there is another trigger: when we see someone else yawning. Yawning is contagious, as they rightly say. Research distinguishes spontaneous and contagious yawning.
It is amazing that animals can also infect each other with yawning. This has been demonstrated in chimpanzees and observed in lion prides. Even between social beings of different species, contagious yawning exists, as a study on the relationship between humans and dogs has shown.
According to research, the purpose of yawning depends on the situation. If one is tired or bored, yawning prepares one to rest. Or it increases alertness. The latter is vital for animals that must always be on their guard. Those who doze off perceive less and react more slowly.
Contagious yawning, on the other hand, is likely to have a social function. Chimpanzees can use it to keep each other awake and alert. Or to express empathy, strengthening their emotional bond: "Yes, I am tired or bored too." A similar phenomenon occurs between humans and dogs.
In lions, explains Wildlife Vets Namibia, contagious yawning can promote "motor synchrony". The pride often acts together. Yawning helps animals coordinate their actions: "Let us prepare to rest, move on, or hunt."