Every dog owner has seen it. Right around dinnertime, a pair of hopeful eyes appears in the kitchen. Or the dog plants itself by the front door just before someone usually gets home. Dogs can't read clocks, so how do they seem to know what time it is?
Here's the short answer. Scientists have found that many animals, including dogs, can estimate and compare lengths of time in ways similar to humans. In one study of pet dogs, the animals greeted their owners more and more intensely the longer they had been left alone, whether the absence lasted minutes or several hours. Like us, dogs also have internal body clocks tied to the daily cycle. Exactly how they experience time is still being studied.
They Notice How Long You're Gone
The study of privately owned dogs is a heartwarming one. Researchers left dogs home alone for different stretches of time and watched what happened when the owners came back. The longer the owner had been away, the more excited the greeting, regardless of how the owners behaved.
That suggests dogs can tell a quick trip to the mailbox apart from a long day at the office. In other words, all that extra tail-wagging after a long absence isn't your imagination.
A Built-In Daily Clock
Nearly all animals have what scientists call a circadian rhythm, a natural cycle that repeats about every 24 hours. The name comes from Latin words meaning around a day. This inner clock helps the body do things at the right time, like sleeping and waking.
Circadian rhythms come from inside the body, but they're fine-tuned by outside cues such as light and temperature. Scientists call those cues zeitgebers, a German word meaning time givers. Daily routines, like regular mealtimes, are part of the world a dog lives in every day.
Size Changes How Time Feels
Here's a fascinating twist. Research suggests an animal's size and metabolism affect how it perceives time. In general, small animals with fast metabolisms, like flies, experience time more slowly than big animals with slow metabolisms. That may help explain why small creatures are so good at reacting to quick events.
Vision is part of this. Scientists measure how fast a flickering light must blink before an animal sees it as steady. Smaller animals with high metabolic rates tend to have higher thresholds, meaning they can notice faster changes.
Super Senses Help Fill In the Clues
Dogs also live in a world rich with information we miss. They have roughly forty times as many scent receptors as humans, from about 125 million to nearly 300 million in breeds like bloodhounds. Their hearing is up to four times sharper than ours. A dog can pick up faint sounds from about 1,300 feet away, compared with about 300 feet for a person.
The most famous example of canine timing may be Hachiko, the Japanese Akita who met his owner at a Tokyo train station each day. Even after his owner died, he kept showing up at the station at the time the train was due, for years.
So while your dog may never learn to read a watch, it's keeping track in its own way. The next time it greets you like you've been gone forever, it might just be telling you exactly how long you were away.
