Light has a clear negative impact on sleep behaviour

Date: 4 September 2015

Introduction: Artificial light has various negative effects on our planet's flora and fauna. Researchers from the University of Antwerp have now shown for the first time that light pollution does indeed disturb the sleep of wild animals. Their article has just been published in Scientific Reports.

When artificial light disturbs the natural light balance of a particular place at night, we can speak of light pollution. This type of pollution is on the increase in our society, a fact which has inevitable consequences for biodiversity and the ecosystem. Previous research has already made clear, for example, that light pollution has negative effects on the reproductive, immune and metabolic systems of both humans and animals.

Scientists from the University of Antwerp set out to investigate the impact of artificial light on animals' sleep. “Like humans, animals need sleep to recover from the stress of the day”, explains Thomas Raap (Department of Biology). “There are strong indications that the health of animals whose sleep is disturbed will eventually begin to decline.”

Raap and his colleagues, Rianne Pinxten and Marcel Eens, set up an experiment on the University of Antwerp’s Drie Eiken campus. “For some time now, this green environment has been home to a large population of wild great tits. They nest and breed in the nest boxes we put up years ago.”

Nest with LED lamp
The great tits' sleep was analysed for two full nights and a comparison made between birds sleeping in the dark and birds exposed to light pollution. The first night, all of the great tits slept in the dark. On the second night, an LED lamp was installed in half of the nest boxes. The other birds were allowed to sleep undisturbed in the dark. Raap and his colleagues monitored the birds and examined numerous parameters, including what time they fell asleep, woke up and left the nest box.

“Birds that slept in nest boxes containing LEDs were awake earlier, lingered more often around the entrance to their boxes and left their nests earlier than the other birds”, reports Raap. “It could be that the light makes them think the sun is already up. During the night, the female birds were awake longer than the males. Our research suggests that the impact of artificial light on great tits is especially clear in the morning. The effects are less pronounced in the evening and at night.

“It's likely that other animals – not just song birds – are affected by light pollution, as it disturbs their sleep and may damage their health. In the future we are planning to do more research, for example on how sleep is affected at different times of the year and the potential consequences of light pollution on the growth of young great tits.”