Dogs may look adorable when they snooze, but their sleeping habits actually hold fascinating clues on how living with humans has shaped canine behaviour. The sleep-wake patterns of the dog can also serve as a useful model for human sleep and wellbeing research.
Domestic dogs have largely diurnal sleeping habits (awake during the day, asleep at night), aligning themselves to the lifestyle of their owners. Most of their sleep happens during the night, between the hours of 9pm and 6am. Unlike humans, however, dogs have frequent bouts of sleeping during the daytime, particularly in the afternoon.
A 2020 study estimated that the average pet dog sleeps for roughly ten hours a day. In reality, it is difficult to determine how much dogs sleep during a 24-hour period because drowsiness (resting with eyes closed) accounts for a considerable proportion of their daily activity. This has led to a large range of estimation (seven to 16 hours) in the amount of time that dogs devote to sleep.
The dog’s ancestor, the grey wolf, tends to show nocturnal (night-time active) or crepuscular (dawn and dusk active) sleep patterns in the wild. That said, wolves can show high variability in their activity, with human disturbance, food availability and weather conditions all influencing their sleep-wake cycles.
Captive wolves, like dogs, typically have a diurnal circadian rhythm, adapting their sleep-wake cycle to the feeding regimes and human activity in their environment. Free-ranging domestic dogs are more inclined to resemble wild canids in their sleep cycles, showing a greater propensity towards crepuscular or nocturnal activity. In urban areas feral dogs may, again, align their sleeping habits with human activity.
These cross-species studies suggest that domestication may not necessarily have changed the sleeping habits of dogs per se. Rather, sleep in dogs appears to be determined by human lifestyle and situational factors. Left to their own devices, however, dogs may be more likely to assume the sleeping habits of their wild ancestors.
The nature of sleep in dogs
Dogs have a number of sleep stages, including drowsiness, lighter non-rapid eye movement (NREM) sleep and deeper rapid eye movement (REM) sleep, where most, although not all, dreaming happens. Dogs devote more of their total sleep time to REM (roughly 2.9 hours a day) than humans (1.9 hours a day).
However, a 2022 study that involved researchers cuddling dogs and socialised wolves to sleep, found that dogs spent less time in REM sleep than the wolves.
Both species, however, spent a similar amount of time in the other stages of sleep. This raises questions about whether REM sleep is related to domestication. Species which are at high risk of being attacked while asleep typically spend less time in REM sleep than animals who live in safer environments, so the findings from this study are intriguing.
Dogs nap during the day more than people or wolves.manushot/Shutterstock
Dogs engage in their deepest sleep during the night, and their daytime naps are relatively light. Like other animals, including rats and hedgehogs, dogs often wake up after a period of REM sleep, perhaps an evolutionary adaptation designed to force them out of their slumber to check for dangers in the environment.
These frequent and relatively brief sleep-wake cycles allow dogs to adjust to changes in their routine more readily than humans. Drug detection dogs, for example, have been found to cope remarkably well with changes to their working schedule, showing little disruption to their sleeping patterns.
As with humans, the duration and quality of sleep in dogs fluctuates, both day to day and over their lifespan. As dogs get older, their sleep becomes more fragmented, accompanied by decreased bouts of REM sleep at night and increased NREM sleep during the day.
Other factors, including canine sex, daytime activity, welfare, environmental conditions, and even social interactions, can affect sleep quality. Deprivations in daytime napping typically lead to quicker sleep onset and longer REM sleep at night, both for dogs and other animals.
Why do dogs sleep?
Scientists still don’t agree why dogs, or indeed other animals, sleep, although we do know that the process is heavily involved in physical restoration.
Memory consolidation (the conversion of short-term memory to long-term memory), closely linked to REM sleep, is perhaps the most studied function of sleep. Most of this work points to sleep’s important role in facilitating learning.
For example, in 2017 researchers in Hungary found that dogs’ memory recall significantly improved when the animals were taught unfamiliar words and then allowed to take a three hour period of sleep and rest.
The nature of sleep in dogs, as in humans, may be influenced by emotional processing. The 2017 Hungarian study found negative experiences, such as owner separation and approach from a threatening stranger, resulted in increased REM sleep and decreased drowsiness in the dogs. Further work on this aspect of sleep is much needed, particularly considering there are close parallels in cognitive functioning between humans and dogs.
Scientists already use dogs as a model for studying a range of sleep-related issues in humans, including sleep disorders, such as narcolepsy and REM behaviour disorder, and age-related changes similar to dementia in humans (cognitive dysfunction syndrome). Although still in its foetal stages, work in this area is starting to yield data that may be useful in helping us decipher early mechanisms for Alzeimher’s disease and treatment for age-related health problems.
It is clear that our dogs are not wasting their time slumbering on the sofa. There is still much to be learned from exploring the biological rhythms of the animals we share our lives with, so let those sleeping dogs lie.
Deborah Wells, Reader, School of Psychology, Queen's University Belfast
This article is republished from The Conversation under a Creative Commons license. Read the original article.
