Can Dogs Smell Time?
Systematic changes in odors may allow dogs to mark the passage of time.
Posted Nov 22, 2019
"You know dogs have some kind of little clock inside of their brain which allows them to tell time"—at least, according to the behavioral biologist who I was chatting with at a scientific conference.
He went on to say, "It's not just their circadian rhythm. [This is a roughly 24-hour cycle in physiological processes that responds to cues like the changes in light and darkness as we go through each day.] I'll give you an example. When I was in elementary school, our family had a rough collie (like Lassie) named Rex. Each morning, Rex would walk the six-block route to school with me and then he would leave me at the door to go back. School ended at 3 o'clock, and when I walked out the door each day to go home, there would be Rex waiting for me. He kept up that precisely timed routine every single school day until he died."
There are historical examples of similar timekeeping abilities in dogs. Perhaps one of the most famous deals with Hachiko, who was an Akita owned by Dr. Eisaburo Ueno, a professor at Tokyo University. Hachiko accompanied his master to the train station each day to see him off. He would then leave only to return to the station each afternoon in time to greet his master. One afternoon, Professor Ueno did not return—he had died in Tokyo. Hachiko waited at the station until midnight. The next day, and every day for nearly 10 years thereafter, Hachiko came to the Shibuya station at exactly the right time to meet the train which his master always used to arrive on.
In both the cases of Rex and Hachiko, the dogs presumably went home after they accompanied their loved one in the morning. They then stayed in the house until they felt that enough time had elapsed so that they now had to leave to meet their human companion on time, in order to escort them home. This means that the dogs had to have a sufficiently accurate time sense to allow them to monitor how long their favorite humans had been out of the house. Do dogs really have that degree of perception of the passage of time?
There have not been very many studies that have tried to answer this question. The best-known was done by two researchers from the Swedish University of Agricultural Sciences in Uppsala. Therese Rhen and Linda Keeling observed 12 dog owners and their dogs. The owners left their dogs alone for increasing amounts of time, and the researchers videotaped how the dogs reacted when their people returned home.
According to their results, the dogs could tell the difference between short and long periods of time, but they couldn't process more specific intervals. They found that the dogs were more excited to see their owners after two hours apart compared to how they reacted if their owner had only left them alone for 30 minutes. However, there was no difference in the dog's reaction after a two-hour absence compared to a four-hour absence.
Nonetheless, there are many hundreds of anecdotal reports where people claim that dogs can tell time well enough to anticipate their owner's return from work each day. The dogs demonstrate this by hovering near the door, or window, perhaps 15 or 20 minutes before their special person is scheduled to walk into the door. Although each individual report is simply an anecdote, the weight of so many similar stories suggests that something real might well be going on here. But if so, what is the cue or mechanism which allows dogs to measure the amount of time that their owner has been away?
Alexandra Horowitz, a psychologist from Barnard College in New York City, believes that she has the answer. She suggests that dogs may well be smelling time changes. As an example, she points out that many dogs can tell which way to follow a scent trail by deciding to travel from where it is weakest (oldest) to where it is strongest (most recent) even though the degree of change in scent intensity might be very tiny over the distance of a dozen or so steps. Since stronger odors are often newer and weaker ones are older, that means that when dogs smell weak odors they are perceiving events of the past. Since dogs can detect both new (strong) and old (weak) scents, it means that they are actually perceiving events that occurred across intervals of time.
So let us now look at the situation where you have to leave the house to go to work each day. Odors change over time, and this usually occurs in a predictable manner. When you walk out of the door the intensity of your scent in the house decreases with each hour that you are gone. It is possible that your dog has learned, through simple repetition, that when your odor has weakened to a specific level, this is when you usually come through the door. In other words, the strength of your residual smell in the house is what is predicting the time when you return home.
Unfortunately, there are no systematic scientific studies that have tested this intriguing hypothesis. However, the BBC television network did set up an informal demonstration which does seem to suggest that it is the dissipation of your bodily scent which is serving as a sort of a clock that allows the dog to smell the passage of time and mark when you are about to return.
The idea behind this demonstration is that if you can somehow renew or refresh the human's scent in the house, then the dog will underestimate the amount of time that has passed and will not be alert and waiting in anticipation at the usual time.
Rehn, T. & Keeling, L. (2011). The effect of time left alone at home on dog welfare. Applied Animal Behavior Science, 129: 129-136. http://www.sciencedirect.com/science/article/pii/S0168159110003242
Horowitz, A. (2017). Being a Dog: Following the Dog Into a World of Smell, Scribner: New York, pp. 336