Why do humans and other mammals yawn?

We yawn, dogs and cats yawn. How come?

Do birds yawn? Crocodiles?

Colibri informed me that even lobsters yawn. Yawning developed very early in the history of life on earth.

I’m subscribed to the Sci-Show youtube channel and last week they had a Quick Questions episode about yawning. Quick summary, it is (possibly) retained as a social signal to the group that you are becoming less alert so everybody else can become more vigilant and alert.

Just for the record, some Straight Dope on yawning.

Although some of this may well be dated by now.

I don’t know about lobsters (how do you tell?) but all vertebrates.


Every time I see this thread title I have to yawn - which is really tricky as I just had a wisdom tooth removed. Ouch. Yawn.

I am owned by three parrots. I can confirm birds yawn.

Yep, and there’s nothing cuter than a sleepy bird yawning.

I have a small hand hummingbird feeder I use a few times a week. The other day a hummer was feeding from the feeder, stopped and looked around a bit then opened his beak with a big yawn. He ruffled his feathers, flapped his wings a few times then went back to feeding. I wish I could have gotten a video, it was just too darn cute.

Except that, at least in humans and I believe in at least some other animals, its effect on other group members is to make them more sleepy.

I think I’ve heard that yawning may be an attempt to increase air intake – a response to a low oxygen level. (Which might explain why it’s common when waking up – switching from sleeping to getting up, needing a higher body oxygen level.)

I know a mechanic uncle who sometimes worked on cars with the engine running inside a garage was warned that increased yawning was a sign of carbon monoxide exposure, and if they noticed several of the mechanics yawning they should immediately check on the ventilation there.

Gotta agree with this one. It’s not that we are tired, per se, that’s why we yawn, but that our respiratory system needs to intake more oxygen for our blood. I think this also applies to animals to some extent, albeit they have different ways of “yawning.”

It can also be a sign of stress, or of tension relief.

In training dogs, a sure sign of stress is a yawn that is not accompanied by a stretch or a lazy moment. These yawns typically have some tension about them too. It’s hard to describe if you haven’t seen it, but generally the dog’s eyes are wide open, the ears either very alert or flattened in fear/submission, and you can see the subtle vibration in the dog’s head and neck at the apex of the yawn.

In horses a yawn after a bodywork or massage session, or even some basic groundwork training, is a good indicator of a release of tension in their body (and mind too). Yawning, licking and chewing, sometimes sneezing are all good signs that whatever is being done is getting through and making relaxing changes.