�ֻ�ֱ��

How do �ֻ�ֱ�� animals sleep in the summer?

More than a month after the summer solstice, Fairbanks is still the land of the midnight sun. Joggers are out getting in their late-night runs along Farmers Loop, and we still don’t need our headlights after another evening ice cream at Hot Licks.

For many of us, the energy boost from summer days is real. We routinely start garden projects an hour or two after bedtime, and it feels like every summer weekend gets booked in the rush before the first snowfall.

Do other �ֻ�ֱ�� animals hustle and bustle as we do in the summer, building nests and storing seeds and hunting and pollinating throughout the night?

Like many science-related questions, the answer is both complex and simple: It depends.

I recently spoke with Cory Williams, an associate professor at Colorado State University, about the different ways Arctic animals respond to the summer sun. Williams received his Ph.D. from the �ֻ�ֱ�� and has spent much of his career studying daily and seasonal animal patterns.

All animals, including humans, have an internal clock that cycles about every 24 hours. This clock — also known as a circadian rhythm — can be “entrained” by an environmental cue, typically the sun.

The way an animal sleeps during the Arctic summer depends on whether the animal is a human, a shorebird, a caribou or an arctic ground squirrel, Williams said.

“Some animals seem to lose the capacity to keep an entrained circadian clock under those conditions,” Williams said. “Humans would fall into that category. There have been a couple of studies on people in the high Arctic and in Antarctica without clocks. Their daily activity period drifts across time as they are unable to maintain a 24-hour rhythm.”

Without clocks, why might people today sleep and wake at odd hours at Utqiaġvik or McMurdo? 

Before dispersing out of Africa, Homo sapiens spent about 230,000 years under more-or-less consistent day-night cycles. Our relatively brief time in Arctic latitudes has likely not been long enough for our internal clocks to be set by subtler daily cues, so we may still rely in part on a predictable day-night cycle to avoid drifting, Williams said.

One such cue is ultraviolet light, which maintains a strong daily rhythm throughout the Arctic summer. UV doesn’t penetrate the lens of the human eye, but some animals might be able to sense its summer rhythm.

“A lot of birds can actually detect light through their skulls, which are thin on top,” Williams said. “They have these deep-brain photoreceptors with the capacity to respond to different wavelengths of light compared to mammals.

“But weirdly, some shorebirds appear to lose their rhythm in the summer until their chicks hatch,” Williams said. That can be caused by continual mate competition, or “reproductive sleeplessness,” a term coined in a paper Williams shared with me.

“And then their circadian rhythm resumes, indicating that the rhythm might not be advantageous until they need to care for their chicks.”

Arctic �ֻ�ֱ�� caribou likely have weak daily rhythms in the summer, Williams said, but their sleep is driven more by their digestion than the sun. As ruminants, they experience about four “rest-and-digest” periods each day, where they briefly sleep. While up and about, they almost continually browse on nutrient-dense tundra to get the most out of the Arctic’s short growing season. In other words, summer is for eating, not sleeping.

If you’re an arctic ground squirrel, summertime activity is centered around midday, and this pattern is maintained even in experimentally constant light conditions. Unlike us, arctic ground squirrels don’t need a sunset to know when to go to bed — they naturally scurry into their burrows to sleep around the same time each night.

(Interestingly, arctic ground squirrels lose any detectable daily cycles while hibernating. Their circadian rhythms resume once the squirrels leave their winter burrows and are first exposed to daylight in the spring.)

So, it depends. Arctic animals respond to constant summer daylight in different ways, and its effects on sleep compete with other influences — sensitivity to different light wavelengths, raising young, digestion and whether they burrow.

Most humans living in Fairbanks avoid the free-running chaos that could result if our clocks were taken away between May and August. The routines of summer — mealtimes, work, summer camps and, for some, �ֻ�ֱ�� Science Forum deadlines — keep us more or less in check, even with the midnight gardening.

Since the late 1970s, the �ֻ�ֱ��' Geophysical Institute has provided the �ֻ�ֱ�� Science Forum column free in cooperation with the UAF research community. Sara Wilbur is a communications coordinator for the Geophysical Institute public information office.