My first night after arriving in New York City in a shaky U-Haul, I was lying in bed, too frazzled to sleep, when I heard something unexpected: not the blaring of sirens or ravings of a street corner madman, but the quiet caw of birds singing in the courtyard behind my building. It was disorienting to hear such clamor — was it actually dawn? I checked my phone and found it was still only 3 a.m., which led me to wonder later — had these urban birds simply adopted that infamous ‘city that never sleeps’ mentality, or was something larger going on?
Artificial light has long been the culprit for many issues: the disappearing night sky, disruption of bird migration patterns and the poor quality of our sleep. Thus, many residents of cities who’ve been woken by noisy avian neighbors were quick to assume that the source of birdsong at night was light pollution. Yet, despite the fact that some researchers support the theory that city lights confuse the birds’ natural body clocks, (thus causing them to be up chirping when they should be snuggled down in their nests), others believe another type of pollution might be to blame: noise.
In a 2007 study from the University of Sheffield in England, researchers measured the noise magnitude of 67 locations around their city. They found that these areas were not only less noisy at night than they were during the day, but were also frequently visited by a very common local bird: the robin. After studying the areas more, researchers found that the red-breasted birds singing at night were the same ones exposed to the highest levels of daytime noise pollution.
So what was the reason for their nocturnal arias? As detailed in the study, the most probable reason is because other robins would be unable to hear them amidst the loud daytime noise. As robins sing for their survival — they call out in order to attract a mate and to assert their territory — the researchers argue that it’s vital for them to go against their biology and stay up to communicate.
That said, there’s still research for the “light pollution” side of the debate: a newer 2015 study from Glasgow University suggests that city lights are confusing the birds’ sense of time and circadian rhythms. A similar 2014 study published in Behavioral Ecology supports the same theory, stating bluntly, “Our results show that artificial night lighting, but not noise, leads to an earlier start of dawn singing [...]”
Yes, many birds have shown some impressive adaptation skills to human-made environments: pigeons — in the never-ending search for crumbs — mill around parks more often than groups of angsty pre-teens, and in Germany researchers reported that nightingales, due to their competition with city noise, have started singing so loudly while searching for a mate that they’re technically breaking sound regulations. But what does all this disruption mean for the many flocks of urban birds?
For starters, while birdsong may be a uniquely peaceful backdrop for some of us night owls, we arguably need to continue monitoring birds’ patterns of singing. Whether the reason for non-nocturnal birds suddenly working the night shift is due to light pollution or noise pollution (or conceivably both?) researchers all agree on one thing: the disrupted natural rhythms could result in a great deal of stress on the urban bird population.
The morning after hearing those birds in the courtyard during my first night in the big city, I woke up regretting not having recorded their surreal singing. Yet, with one quick search, I was able to find a recording of a mockingbird singing at 2:30 in the morning in NYC that is very much reminiscent of my experience. Have a listen, but perhaps at a less jarring hour: