Across much of our planet, truly dark nights are becoming a distant memory. From the bright glow of city streetlamps to the vibrant pulse of neon billboards, artificial light has effectively blurred the natural boundary between day and night.
A significant global study, analyzing over 60 million bird vocalizations from 583 species, has revealed a stark consequence: birds in artificially lit environments are staying active for nearly an hour longer after sunset than their counterparts in darker areas.
Dr. Brent Pease, the lead author and an assistant professor at Southern Illinois University Carbondale, remarked, “I know how I feel when I lose an hour of sleep. This can’t be a great situation. But the picture is complex.” He acknowledges the intricate nature of this issue.
Scientists are raising alarms about this behavioral shift, warning that it disrupts birds’ vital natural rhythms, impacting their migration, feeding habits, and breeding cycles. Such widespread alteration invariably destabilizes food chains and entire ecosystems.
Dr. Pease’s journey into this research began with a simple teaching idea: introducing students to birds through their unique songs. He deployed basic sound recorders and small computers to capture avian calls. It was during this process that he discovered a volunteer-driven platform where bird sounds, identified by artificial intelligence (AI), were being shared.
He recounted his surprise, stating, “I couldn’t believe what I was seeing. There were thousands of sound recorders, all across the globe.”
Pease compared this discovery to the transformative impact of trail cameras on mammal studies. These motion and heat-triggered devices revolutionized research by uncovering behaviors, from nocturnal leopard prowls to dawn deer grazing, previously hidden from human observation.
Similarly, BirdWeather, an acoustic network powered by volunteers and analyzed by an AI model called BirdNET, has revolutionized bird research by automatically logging and identifying songs across continents.
The Twilight Chorus Extends
Co-author Neil Gilbert, a postdoctoral researcher at Oklahoma State University’s Department of Biology, shared his specific interest: “Light pollution in particular has been interesting to me. I’ve thought a lot about how animals are responding to stressors and especially behaviour timing.”
Dr. Pease enlisted Gilbert to collaborate on studying the impact of artificial night light on bird behavior. Together, they utilized this global network of volunteer-placed microphones and sensors in diverse environments, creating a real-time map of avian activity.
The researchers honed in on two key daily markers: the first song at sunrise and the last at sunset. To determine species vulnerability, they also considered factors like eye size, nest construction, migration routes, and specific habitats. This comprehensive data allowed for a direct comparison between bird activity in brightly lit and naturally dark regions.
Their findings clearly indicated that light pollution significantly extended the active hours for birds.
Through the analysis of millions of recordings from hundreds of species, predominantly from the U.S., Europe, and Australia, the study definitively showed that artificial light was causing birds to remain awake for almost an additional hour.
Gilbert expressed his astonishment: “We were pretty surprised by the size of the effect. Fifty minutes as an average across species was quite a bit more than what we were expecting.”
However, not all avian species reacted to artificial light with the same intensity.
Birds possessing larger, more perceptive eyes exhibited the most significant changes, beginning their songs 35 minutes earlier at dawn and extending them 56 minutes later into dusk in illuminated zones. In contrast, small-eyed species largely maintained their usual routines. Open-nesting birds, more exposed to the artificial glow, were more affected than those nesting in cavities. Migratory birds also displayed greater disturbance than their sedentary counterparts. These shifts were particularly pronounced during the crucial breeding season.
While some species prolonged their activity by two hours and others by only a few minutes, the overarching pattern was undeniable: brighter nights consistently correlated with unnaturally extended ‘days’ for birds.
Dr. Pease highlighted the implications, stating, “If they’re spending an extra hour of time… they’re going to need more additional caloric intake for all this extra activity that they’re doing.” He also acknowledged a potential upside: “But this additional extra hour of activity can also result in an increased foraging time and potentially even increased reproductive output.”
The Disruption of Darkness
Anusha Shankar, an integrative biologist at the Tata Institute of Fundamental Research, Hyderabad, who studies organisms through diverse biological insights, underscored the significance of this research.
Dr. Shankar elaborated, “Every organism that we know of on Earth, every animal, even many plants, and phytoplankton — they all have some sort of sense of time. And a lot of that comes from light cues.”
Artificial light ruthlessly disrupts these ancient, natural cycles. A tragic example can be seen in Indian cities, where birds frequently die from collisions with brightly lit glass facades, transforming gleaming office buildings into fatal traps.
She concluded, “So if you disrupt these ancient rhythms, everything gets messed up.”
Such ecological mismatches can be particularly devastating for migratory birds. Their journeys are precisely timed to align with seasonal food sources, which themselves rely on light cues. If plants bloom prematurely or insects emerge belatedly, these finely tuned migrations, honed over millennia, can become tragically perilous.
Filmmaker Sriram Murali advocates for preserving natural darkness for the benefit of humans, animals, and celestial observation. Through his extensive research and films on fireflies, Murali has championed the cause of raising awareness about light pollution, often referring to these bioluminescent beetles as the ‘flagship species of the night.’ Fireflies, in particular, rely on intricate flashes of light to attract mates.
In the forests and villages of southern India, the mesmerizing synchronized twinkling of fireflies appears for a short period in May and June, immediately after sunset. On their most active nights, entire groves glisten with their distinct green-gold pulses, resembling magical fairy lights. However, artificial lighting disrupts this crucial communication, severely hindering their ability to find mates and survive.
Mr. Murali underscored the broader implications, stating, “We know that exposure to lighting affects the circadian rhythm” – referring to our natural biological clock governing sleep and wakefulness. “Doctors know it and we are careful about it for our own children. So then the question is, how do we teach people empathy and bring about change?”
A Simple Solution
The ultimate impact of extending a bird’s active day—whether it’s a benefit or a detriment—remains unclear. While increased time for feeding and mating could be advantageous, reduced rest periods might prove harmful.
Fortunately, unlike many other pervasive human impacts, light pollution is entirely reversible. Practical solutions include shielding streetlamps, dimming billboards, and simply switching off lights when they are not essential.
Dr. Pease emphasized that combating light pollution doesn’t demand the extensive investments or prolonged restoration efforts associated with issues like climate change or habitat destruction.
He concluded optimistically, “If light pollution turns out to be a negative thing for bird populations, we can do a behavior change across the globe to turn out the lights and make the night dark again. We’re just a light switch away here.”