We all know just how catchy yawning can be, and it turns out so does the humble budgie.
Contagious yawning is the spreading of a yawn from person-to-person, animal-to-animal, and even human-to-animal in an unconscious gaping-mouthed Mexican wave.
A study published in the journal Animal Cognition shows that contagious yawning occurs between budgerigars (Melopsittacus undulatus), also known as parakeets.
This backs up previous observations of the behaviour outside the lab.
If confirmed, it suggests that these popular pet birds are empathic. That is, they can put themselves into another animal's shoes and imagine what it is feeling.
Native to Australia, budgerigars are highly social parrots. They form lasting bonds between mates and fly in large coordinated flocks.
Until now, contagious yawning had only been documented in humans, chimpanzees, domesticated dogs and lab rats. The budgie is the first non-mammal to exhibit the behaviour.
Researches at the State University of New York paired 16 of the birds in adjoining cages. In some cases the budgies could either see each other, while in others they could not.
In a second experiment, the birds were shown video footage of their fellow budgies yawning and not yawning on screen.
If yawning was contagious, the researchers reasoned, they would only see clusters of yawns when the budgies were looking at each other.
The budgies yawned three times as often within a 5-minute window when the birds could see one another than when their view was blocked.
Also, they yawned twice as often when they viewed video clips of yawning budgies.
No one knows for certain why we yawn. Most backboned animals ("vertebrates") do it. One idea is that it wakes up the brain by lowering its temperature.
However, contagious yawning appears to be more than just an involuntary action.
Instead, it is a primitive form of showing empathy. It has been found to be more common among more empathic people.