WEDNESDAY, Oct. 24 (HealthDay News) -- If you're yawning from fatigue or boredom, your loyal dog is likely yawning as well, a new study finds.

But this isn't the case with puppies of 7 months or younger, who may not have developed empathy yet. (And they're far too busy chewing up shoes or jumping on the furniture.)

Researchers in Sweden explained that dogs, like humans, gradually become susceptible to yawns as they get older. They noted that contagious yawning is a sign of empathy, as well as a response to being tired or bored.

The researchers, led by Elainie Alenkaer Madsen and Tomas Persson at Lund University, observed the response of 35 dogs between 4 and 14 months old during play and cuddling when a human repeatedly yawned, gaped or did neither.

The final analysis only included 32 dogs. "Three dogs were excluded from analyses, due to, respectively, distractions, over-excitedness and poor owner yawning," the researchers wrote.

Dogs older than 7 months showed signs of contagious yawning. The study also showed that roughly half the dogs became tired themselves, so much so that some dogs needed to be prevented from falling asleep. The researchers concluded that empathy slowly develops over the first year of a dog's life.

Children also typically start to yawn contagiously at the age of 4 years, when their ability to accurately identify other people's emotions is more developed. Unlike humans and other primates, however, adult dogs do not respond differently to strangers and are just as likely to catch yawns from people they don't know very well.

The study was published online Oct. 17 in the journal Animal Cognition.

More information

Utah State University has information about teaching empathy.