Nocturnal light makes birds change their behaviour

Songbirds change their behaviour and timing when nestboxes are exposed to artificial light at night. "They become light sleepers, literally and metaphorically", says Maaike de Jong (NIOO-KNAW). She successfully defended her thesis on the effects of different colours of light at Wageningen University on Friday. The most surprising effect she's found? Some birds are forced to become more monogamous...

Compared to white or red light, green light has a much friendlier ring to it. It's used in many places to mitigate 'light pollution'. But according to Maaike de Jong that doesn't necessarily work.

She's been studying the impact of artificial light on nesting behaviour as part of the LichtOpNatuur project ("Light on Nature"), led by the Netherlands Institute of Ecology (NIOO-KNAW) and funded by the Netherlands Technology Foundation (STW).

Disrupted timing

Birds have excellent eyesight, and their brains respond strongly to light. That makes them perfect test subjects for a project that studies the gradual disappearance of 'real' darkness from our living environment.

De Jong focused mostly on great tits, blue tits and pied flycatchers. She found that exposure to artificial light of any colour - be it white, red or green - caused major disruption to the birds' timing.

Although the exact effects were different for each colour, they all had in common that the light caused the birds to become active about two hours earlier than normal. And they no longer slept uninterruptedly, taking moments of rest during the daytime to compensate for their day's increased length.

Nocturnal escapades

In terms of the overall nesting season, the changes in behaviour also affected the moment the birds started laying eggs. In the cold spring of 2013, the birds laid their first eggs several days earlier than in other years when they were exposed to either white or green artificial light at night.

And in the 2014 season, De Jong found that another thing being affected was the birds' appetite or energy for adulterous nocturnal trysts.

Nests close to white and red light, especially, were found to contain fewer young that were born 'out of wedlock'. This may in the longer term affect processes of natural selection that favour variety in sexual partners.

Ongoing project

It's not clear yet whether the disruption observed by Maaike de Jong also affects population numbers. "It may take years before we can draw any reliable conclusions in that respect." That's why the project will be continued.

One other aspect of the issue De Jong says should definitely be studied is urbanisation: city birds are after all known to be quite opportunistic. "They can adapt to new situations when it suits them."

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With more than 300 staff and students, the NIOO is one of the largest research institutes of the Royal Netherlands Academy of Arts and Sciences (KNAW). It specialises in terrestrial and aquatic ecology. As of 2011, it is located in an innovative and sustainable research building in Wageningen.

For more information:

• Maaike de Jong, Department of Animal Ecology NIOO-KNAW, tel. +31-6-40322323, maaike.dejong@live.com
• Froukje Rienks M.Sc., Science Communication Officer NIOO-KNAW, tel. +31-6-10487481 / +31-317-473590,f.rienks@nioo.knaw.nl