Does daylight saving time affect dogs? It depends if they have to work.

Daylight saving time - that pesky, controversial human invention that almost two-thirds of Americans say they want to get rid of - is associated with health problems, sleep loss and “social jet lag” in humans. But what is the impact on our canine best friends?

It might depend on their age - and, crucially, whether they are a working dog, a new study suggests.

Daylight saving time (DST) is observed in about one-third of the countries around the world, with clocks changing one hour forward in spring and one hour back in fall to keep human work and sleep patterns in sync with daylight hours.

Studies show the change can lead to disruption in human sleep patterns for about one week afterward and even cause a short-lived increase in traffic accidents. However, there is little understanding of how “this sudden, human-mitigated change” affects companion animals, as well as the implications for animal care, researchers at the University of Toronto’s department of anthropology wrote in their new report, published in the PLOS One journal Wednesday.

The researchers carried out what they described as the first study into the impact of DST on the activities of dogs, using motion-sensitive watches to monitor the activity and working patterns of 25 sled dogs in Ontario, as well as 29 pet dogs and their human caregivers, in the week surrounding the fall DST change in November 2021.

“Anecdotally, everyone you talk to will mention, ‘Oh, my cat was up at 6 waiting for her breakfast, or my dog was scratching at the door, even though we were allowed to sleep in an extra hour,’” researcher Ming Fei Li said in an interview. Hence, Li said, she was surprised at some of the study results - which found that companion dogs did not seem to show “any patterns of daylight saving time adjustment,” although the working sled dogs needed a day to adjust.

The dogs involved were huskies or malamutes, chosen for their lineage that can be traced back to Siberia and association with sledding. The study was carried out as part of a wider research project into the domestication of dogs, and the animals were based at Haliburton Forest & Wildlife Reserve, while the pets were located in Ontario and Quebec. Those with medical issues or over 13 years old were excluded.

The researchers tracked activity levels in the working dogs in the hour around sunrise, which changed from 7:50 a.m. to 6:50 a.m. with DST, as well as the arrival time of the sled dog handlers, at 7:30 a.m. For pet dogs, activity was tracked at sunrise and around the wake-up time of the human caregivers in the days before and after DST came into effect.

Data showed that on the Sunday DST came into effect, the sled dogs were “significantly more active” before their handlers arrived but returned to pre-DST levels of morning activity in the following two days. By contrast, the pet dogs showed no change in their morning activity levels based on sunrise time, on either the first day of DST or the days after, despite their caregivers waking up earlier on weekdays after DST came into effect.

Age was also a factor in the way the animals responded to the clocks changing, with older pet dogs less active on the first morning after DST came into effect. “We recommend caregivers of older dogs to be especially mindful in implementing sudden changes to daily routines,” the researchers said.

The researchers said overall they were surprised at how easily the dogs adapted.

“The takeaway from our research might be that if we would like to make the transition a little bit easier, perhaps having a more flexible routine can help with that,” particularly with older dogs, co-author Lavania Nagendran said in an interview. “But it does seem that even if we do have these really strict routines, they tend to adjust quite quickly.”

The report’s findings about the impact of DST on older pets tracks with what we know about humans, said Jeffrey Kelu, a postdoctoral research associate at King’s College London specializing in circadian rhythms, who was not involved in the research, adding: “We know that in the elderly, circadian rhythms are less robust.”

Kelu advised pet owners worried about how DST could affect their animals to introduce changes gradually. “It’s good to prepare around a week in advance for the change. For example, you start to feed your dog 15 minutes early, 30 minutes early, 45 minutes early to kind of prepare them for it so it will be less upsetting for them,” he said.

The latest research also raises questions about the impact of sunlight on dogs’ internal clocks.

Li said she had expected an “association between sled dogs’ morning activity and sunrise time,” particularly because they were “outdoor-housed dogs,” rather than the companion dogs, who mostly slept indoors with their owners. However, the findings suggested “they were only aligning their morning wake-up time to handler arrivals, not to sunrise.”

Kelu described sunlight as “the strongest synchronizing factor that can affect your body clock” and said pets are also highly influenced by human beings.

The study had some limitations, including the individual variability among the companion dogs and their schedules. The authors noted the study took place during the covid-19 pandemic, when many people were working from home, which may have allowed for greater flexibility in the human caregivers’ wake-up times. It also did not account for the activities of other people in the household.

Nonetheless, researchers say the findings serve as a reminder of the impact that humans have on dogs in their care - whether they are working sled dogs or companion dogs. “Many studies have shown that the activity of companion dogs strongly aligns with human routines, perhaps more than endogenous environmental variables,” the report said. “In our study … this was also the case in outdoor kennel-housed sled dogs whose activities adjusted according to handler arrival time rather than sunlight.”

The study’s survey results also “indicated that dogs were spending the majority of their time with humans irrespective of the primary caregiver’s working commitments,” the study said, noting that “more than half of the dogs spent less than 5 hours alone daily.”