How does 24 hour daylight impact animals in the far North?
Animals seem to adapt successfully to life under the midnight sun
This week's question comes to us from Genevieve Willis who recently spent her first Summer in Inuvik, where she experienced the midnight sun for the first time.
She asks:
With 24 hours of daylight, I've noticed birds chirping at all hours of the day and night. I was wondering how the constant daylight affects birds and other animals who usually have a day/night sleep cycle?
Jeff Lane, a wildlife biologist from the University of Saskatchewan explains that disruption of circadian cycles by the onset of constant daylight affects different species in different ways. Circadian rhythms are initiated by the circadian clock which is found in the brains of birds and mammals, including us. The clock generates signals that occur on an approximately 24 hour cycle, but it also receives light information from the retina. Those daily patterns of light modulate the clock to daily conditions of day and night. Misalignment of the rhythmic signals from the clock and light patterns can be disruptive. In humans, this explains jet-lag.
Some northern species, such as reindeer and ptarmigan in Norway, the absence of obvious light/dark cycles have no impact. These animals do not show behavioural patterns that align with a typical 24 hour circadian clock.
Other species, such as Arctic ground squirrels in Alaska and honey bees in Finland have been shown to exhibit 24 hour circadian cycles. It is believed that these species are able to maintain the cycles because they can perceive variations in the quality and intensity of light that exist even though the Sun remains above the horizon.
There may be costs for animals who normally have a day/night sleep cycle. It is not well studied, but it is thought they may be exposed to more nocturnal versus day active predators. But there may also be benefits, particularly for birds living in 24 hour daylight. Because bird song is meant to attract mates, those males making calls earlier in the day than their competitors, may be more attractive to a potential mate.