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Oct 3, 2018

Robins: confused by the light?


Amanda Scott, Dark Sky Advisor with Cranborne Chase AONB, looks into whether light pollution is the reason behind night-singing robins.

A few years ago, I was living in South East London. London is surprisingly green, so I enjoyed the woods and nature reserves close to home. Especially, however, I loved to watch the birds at the bird table in my garden. One of my favourite avian visitors was a feisty little robin, which once famously saw off a whole gang of starlings in order to protect what it considered its own personal feeding station.

Among the main downsides of London, however, and indeed any city or large urban sprawl, is light pollution. Looking upwards on a ‘clear’ night only a narrow circle of a few stars is visible, and no part of the sky is unaffected by the city glow. That was a shame for me and other human city-dwellers, but what about my friend, the robin? On several nights, I would wake up in the small hours and listen to it singing its heart out from a bush under a nearby streetlight. It might have cheered my wakeful nights with its bright song, but was this good for the robin? Robins are the first birds to pipe up in the dawn chorus and among the last to finish singing at dusk, but why was this daytime bird singing in the middle of the night?

When promoting dark skies for Cranborne Chase AONB became my job, I remembered my nocturnal robin and decided to do a little research. The first thing I discovered is that it might not be all about the light. Fuller et al. (2007) found that urban-dwelling robins sing at night to avoid competition with the city’s daytime cacophony of sounds; the authors also concluded that the effect of artificial light pollution was much weaker than noise. Do a Google search, and you will find other research pointing in this direction. Robins are indeed adapted to continue being active well into dawn and dusk (their large eyes, in comparison with their overall size, are an adaptation to hunting for food in the crepuscular gloom). In his book The Robin: A Biography, Stephen Moss notes that night-time singing by robins may in fact not be new in our brightly lit and noisier age, quoting RD Blackmore’s statement in Lorna Doone that “Everyone knows that robins sing all night” (Moss 2017).

Other research, however, finds a much stronger causation effect from artificial light at night (ALAN). The robin’s large eye, again, is suggested as a reason, because it means it is particularly sensitive to light (which is good for crepuscular foraging), but especially sensitive to blue light (not so good for being disturbed by artificial light at night, which is all too often in the blue/white spectrum). Dr Davide Dominoni, a researcher at the University of Glasgow, has studied the ecological and biological effects of ALAN on songbirds, including the fiercely territorial robin, and points to blue spectrum artificial light as confusing robins into singing too early, believing it is dawn and therefore time to start defending their territory (Dominoni 2015). This would expend energy at a time normally spent resting. While we can take time out to recover from a late night out, robins and other diurnal songbirds can’t have a lie-in – after a bout of midnight singing, they still need to keep going through the day, and this can have long-term effects on their fitness.

Another recent study also pointing to the influence of ALAN, this time by scientists at the Max Planck Institute for Ornithology in Germany (Da Silva et al. 2015), considered the ecological implications of artificial lighting on dawn and dusk singing for six songbird species: the European robin, common blackbird, song thrush, great tit, blue tit, and common chaffinch. They found that ALAN altered natural seasonal rhythms in these species, with four of the study species (including the robin) advancing the time of year at which they sang at dawn and dusk in the presence of artificial night lighting.

It is not unusual to find seemingly contradictory research results in a comparatively new area of study such as the impact of artificial lighting. The nature of science is to build up a body of research, with different studies considering different aspects until a fuller picture begins to form. In the case of biological organisms, this picture will often be complex, highlighting numerous influencing and interacting factors. I suspect the truth probably lies somewhere in disturbance from both light and noise contributing to my urban robin’s night-time song.

My ‘take-away’ thought is that Cranborne Chase AONB residents and those living in nearby, more heavily light-polluted areas, are indeed fortunate to have access to such wonderful dark skies and a tranquil countryside in which we, and the robins, can live, eat, and sing in peace.

 

References:

Da Silva A, Valcu M and Kempenaers B (2015) Light pollution alters the phenology of dawn and dusk singing in common European songbirds. Philosophical Transactions of the Royal Society B 370: 20140126

Dominoni DM (2015) The effects of light pollution on biological rhythms of birds: an integrated, mechanistic perspective. Journal of Ornithology 156: 409–418

Fuller RA, Warren PH, Gaston KJ (2007) Daytime noise predicts nocturnal singing in urban robins. Biology Letters 3: 368–370

Moss S (2017) The Robin: a Biography. Vintage Publishing, UK.