Passers by may have thought it a little odd. It is not every day they see a man crouched under bushes in the garden at dusk clutching an iphone. The reason for this madness was that I was intrigued by a paper* in Proc. Roy. Soc. on the effect of artificial light at night on reproduction in birds.
When I first saw the title my immediate thought was that there was nothing new. Since Rowan described what happened to starlings under London street lights in 1938, I thought I would be reading of something very similar. However, this new paper is concerned not with the typical levels of light that are known to advance reproduction in photoperiodic birds but with what happens with the low light intensities present in urban environments at night. First of all, they measured the intensity of light at night in urban and rural environments and then exposed blackbirds (Turdus merula) from cities or forests to either darkness or the low intensities typical of an urban environment at night. In short, the reproductive system developed earlier, and moulting occurred sooner, in birds exposed to low-intensity light (only 0.3 lux) at night. The authors concluded that light pollution is having an effect.
But then I began to worry. Is there something special about the blackbird? On those very early mornings when I had to set up for the airport with virtually no light in the sky, I often disturbed blackbirds already up and looking for worms in the garden. No other birds were active at that time. So, is the whole array of garden birds affected by the light pollution: chaffinches, house sparrows, greenfinches, starlings etc?
Then I began to wonder how is the low intensity of light perceived. Most birds here sleep with the heads tucked under their wings, some, the wren for example, in opaque nests. Would even extraocular light receptors be exposed? Do the birds wake at intervals to see if it is light enough to feed? And does even the low light then act through the usual photoperiodic channels?
That’s why I have crawling around the garden with my iphone. It has the LuxMeter app and that is showing me what the light intensities are when birds are active. But then I realised that in large parts of the northern hemisphere, including here in the West of Scotland, it never really gets dark in the summer, so that any effect of artificial light pollution could only be exerted in the short winter nights.
My (nearly) final thought was what happens to birds that are classically considered to be non-photoperiodic (like the estrildids in the tropics) in light-polluted cities. Do birds in the cities there have longer periods of activity and feeding and is there any other physiological effect?
And, really finally, is there any effect of the moon (0.25 lux on a clear night at full moon)?
*Artificial light at night advances avian reproductive physiology. Dominoni, D, Quetting, M Partecke, J. 2013. Proc. R. Soc. B 280, 20123017.
