Dear Sam,

Dogs might not use clocks to tell time like humans do, but they are pretty good at following a schedule. They often know when it is time for a walk, dinner, or sleep.

A lot of animals rely on something called a circadian rhythm, a 24-hour cycle, to help them figure out when it is time to do different things. This system is sort of like an inner clock.

That’s what I found out from my friend Lynne Nelson, a veterinarian and researcher at Washington State University who takes care of lots of animals.

The circadian rhythm system is controlled by light. Humans’ ability to sense light is part of the reason why they are awake and alert during the day. And that’s why when it’s dark out, they go to sleep.

Dr. Universe, a grey cat with a lab coat, in a hero poseDifferent animals can have slightly different circadian rhythms. Cats, for example, are diurnal animals. They go out at night and sleep a lot during the day.

In a way, humans have helped dogs learn to tell time. When humans train dogs, dogs learn how to interact with both their humans and their environment.

“Dogs are training their brains based on different events, like owners coming home or when the food is going to come out,” Nelson said.

She also told me about something called entrainment, or the interaction between an animal’s circadian rhythm and the environment. You can think of it sort of like the way your stomach growls to signal that it is almost time for lunch.

“Dogs and cats know when they normally eat. So, they start to get hungry before then and start to bug their owners—even before they put the food out,” Nelson said.

All these things are entrained based on certain genes that control the development of different traits, as well as wiring in our brains, Nelson said.

“It all goes on in our brains and it happens without us even anticipating or knowing,” she adds.

There are some animals that not only have daily schedules, but seasonal schedules. We see this in animals that migrate or hibernate. They get cues from nature in the form of daylight and temperature. As winter approaches, bears know it is time to make their move because days get shorter and the air gets colder.

Nelson is really curious about bears. She said bears are really good at knowing schedules, including when it is the best time to get into people’s trash cans. They use clues from their environment, along with their circadian rhythms, to know when humans will put out the trash. Then they can look for a snack.

“Animals that are food-motivated like dogs and bears can become especially attuned to telling time because of special treats,” Nelson said.

When dogs aren’t eating or playing, they spend a lot of their time sleeping. Dogs sleep for around 14 hours or so a day. No matter the hour, it is almost always prime time for a nap.

Dr. Universe