In humans, artificial light can affect sleep. Blue rich light appears white and disrupts sleep, whereas blue reduced light appears amber and may not disrupt sleep. But in animals, we do not have as well of an understanding of the effect of artificial light on sleep. This study measures the brain activity of birds that have their sleep disrupted with white and amber light. In some species of birds, the blue light causes many sleep issues and the amber light did not cause as many or any sleep problems. However, in some species, both amber and white light disrupted sleep.
This study aims to see if white and amber light has the same effect on the sleep cycle of birds as it does in humans.
Results and Methods
White Light and Pigeons
This was a three night experiment. The first night the pigeons were not exposed to any light, the second night they were exposed to a white light, and the third night they were not exposed to any light. During the treatment night, every aspect of sleep that was measured was disrupted, including amount, composition, intensity, and continuity. After the 24 hour recovery period, the pigeons eventually returned to normal sleep, but did not make up for the sleep lost during the light treatment night.
Amber Light and Pigeons
In this experiment, the pigeons were either exposed to white or amber light, and then after 4 to 6 days, the birds in the study were treated with the opposite type of light. The white light results aligned with the results from the last study, but the amber light results were unexpected. The amber light also disrupted the sleep of the pigeons in the same way that the white light did.
American Magpie Versus Pigeons
American Magpie birds were also tested with white and amber light to see how they responded in comparison to the pigeons. But in this experiment, the light treatment was only done for the first third of the night to allow the birds to recover through the night. This time, there was a difference between the white and amber light. The non rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep were decreased in the 4 hour white light treatments compared to the amber light. There was also a significantly greater disruption of sleep in the American Magpie birds (they lost 76% of sleep under white light) than in the Pigeons (they lost only 44% of sleep due to white light). The American Magpie did not have a recovery in the REM sleep, but did have a recovery in NREM sleep which is unlike the Pigeon results. During the following night of sleep, the American Magpie sleep almost returned to the baseline levels.
This study shows that artificial light does disrupt the sleep of birds. In American Magpies, the amber had no effect of NREM sleep and less effect on sleep than the white light. But, Pigeons were equally affected by white and amber light. Due to these results, we can conclude that the effect of artificial light colors on humans is applicable to some birds, but not all. There are explanations for this finding. First, light that resembles natural light may cause a different response in different species, which can depend on ecology. Next, the birds living in captivity may have an effect on their response to artificial and natural light. And third, different species may have different circadian rhythms that are affected differently by lights at night. For example, the regulation of the circadian rhythms may be due to light receptors in some species, but not in other species.
This study does not predict how the light affects the sleep of different birds, but does show that light may be important in the physiology of sleep and regulation of the circadian rhythm in birds and other animals.