The summer solstice is the longest day of the year in the Northern Hemisphere. In other words, today is the day with the most daylight hours in the Northern Hemisphere.
This happens when the Earth's tilt toward the Sun reaches its maximum and the Sun points directly at the Tropic of Cancer.
If people in the northern latitudes don't look at the clock, the prolongation of the day may make it difficult for them to know when to fall asleep, but the midnight sun is not a problem for many other animals.
On this day, a full 24 hours of daylight is provided over the Arctic Circle, and people in the Northern Latitudes celebrate with special events, such as live broadcasting at the moment when the winter solstice begins at Stonehenge in England.
But, according to a study published in the Journal of Physiology, without a watch, people may neglect bedtime because humans look at time badly during most light or most dark periods.
This is because light has a large impact on the body's circadian rhythm or sleep-wake cycle.
But Corey Williams, a biologist at the University of Alaska's Fairbanks University, says many animals in the Northern Latitudes can naturally control their sleep-wake cycles under extreme daytime conditions.
"Some animals no longer sleep for long periods of time," Williams said, "and at this time of year, they abandon their usual daily rhythms."
For example, small brown and white shorebirds that breed over the Arctic Circle — the half-petaled spoonbill — are not disturbed by prolonged daylight.
They alternate sleep and wake up with their nesting buddies all day long.
Williams said: "When males are active, females are in the nest and vice versa. ”
"It's not on the 24-hour schedule."
During the summer months, reindeer also overlook the absence of a chiaroscuro cycle.
Instead, their sleep cycles are governed by extreme rhythms, meaning they sleep when they need to digest food.
Williams said: "They lost their normally long sleep. ”
"They take a lot of naps during the day instead of a concentrated sleep."
This only occurs in polar species because their behavior is not affected by the light-dark cycle.
At this time of year, the advantage of the animal's activity at a particular time of day disappears.
For example, foraging at night neither saves energy nor protects itself from predators, because it is always daytime.
But not all polar species have abandoned their circadian rhythms.
Arctic ground squirrels, for example, stick to their sleep schedules throughout the year.
To save energy, they retreat into the caves during the darkest part of the day in the summer (still not as dark, more like dusk).
As global average temperatures rise, animals are migrating to higher latitudes, "so it's going to be interesting to see how animals that aren't exposed to polar environments react as they migrate north." ”