by Bimla Kumari
Have you ever woken up in the middle of the night, convinced it was morning, only to discover the clock said 2:00 a.m.? For a moment, your sense of time fades. Something doesn’t feel right.
Now imagine that confusion lasting every night. For many birds living under artificial light, something similar may be happening. Once consistently directed by sunrise and sunset, their perception of time is subtly changing.
That shift may already be visible around us. In many towns and cities, it is no longer unusual to hear birds calling long before sunrise near brightly lit streets and buildings.
For birds, light does more than simply illuminate the world around them. It is one of the cues they use to keep track of time. Light helps regulate their circadian rhythms, the internal 24-hour cycles that determine when to wake, feed, sing, and rest. These rhythms are closely aligned with the natural cycle of day and night. As daylight increases, birds become active, while the fading light of evening signals a time to slow down and rest.
Artificial light at night is beginning to interfere with these natural cues. Streetlights, buildings, and traffic continue to glow long after sunset, creating a subtle skyglow [2]. To a bird, this extra brightness can feel like an extended twilight or an early start to the day.
But how widespread is the effect?
To find out, researchers Brent S. Pease of Southern Illinois University and Neil A. Gilbert of Oklahoma State University analysed millions of bird vocalisations collected by automated acoustic sensors across the globe. With the help of machine learning, they tracked the daily activity patterns of hundreds of species across thousands of locations [4].
Their study, published in Science, revealed a striking pattern: birds exposed to brighter nights remained active for about 50 minutes longer, on average, than those living under darker skies. Rather than ending their day after sunset, birds remained active well into hours that would normally be spent resting. Not all birds respond to artificial light in the same way. Birds with larger eyes are more sensitive to low levels of light and may therefore be more strongly affected by it, while species with open nests are exposed to artificial glare for longer periods. Migratory birds, which rely on environmental cues to guide their seasonal movements, may be particularly vulnerable. These effects are often most apparent during the breeding season, when timing is critical [4].
At first, this extended activity might not seem harmful. More time awake could mean more opportunities to forage or communicate with others. But every extra hour of activity comes at a cost. If birds stay active longer without finding enough additional food, they may end up spending more energy than they gain which, over time, can affect their health, reproduction, and survival.
There are also long-time ecological consequences. When birds begin their day earlier or end it later, then predation, competition and feeding patterns can shift. The boundary between day and night, once clearly defined, gradually begins to blur.
What we are seeing in birds is just one part of a much larger pattern. Birds are not the only creatures affected by brighter nights. Artificial light now reaches much of the planet, and its glow continues to spread. From insects drawn to lamps to mammals shifting their daily routines, many species are now adapting to this continous glow [1, 5]. Individually, these changes may seem small, but together they are reshaping the rhythms of entire ecosystems as if countless clocks, once synchronised by the rising and setting of the sun, are beginning to drift apart.
Although artificial light has brought many benefits to human life, from safer streets to greater convenience [3], its impact on the natural world often goes unnoticed. The goal is not to eliminate artificial light completely, but to use it more thoughtfully. Shielding lights, reducing unnecessary illumination, and choosing warmer, less intense lighting can help make the night a little darker for wildlife while preserving some of the natural rhythms that many species still depend on.
So the next time you notice a bird singing under a streetlight long before dawn, you may be witnessing more than an unusual behaviour. For many species, night is no longer as dark as it once was, and the rhythms that once followed the rising and setting of the sun are beginning to shift.
Author
Dr. Bimla Kumari earned her Ph.D. in Plant Pathology from G. B. Pant University of Agriculture and Technology, Pantnagar, and works on plant health and agricultural systems, including integrated pest management (IPM), phytosanitary regulations, and quarantine. Her work spans plant–microbe interactions, disease management, and molecular diagnostics,
with a focus on building more resilient and sustainable agriculture. Outside work, she finds joy in gardening, bird watching, photography, and writing—often discovering quiet stories hidden in nature.
Illustrator
Anwesha Pal completed her master’s in Inter-disciplinary Biosciences from JNCASR, Bengaluru. She has been trained in molecular biology, gene regulation, and cytogenetics during her academic journey.
She is passionate about studying ageing and age-related disorders with a goal to work in the area to improve the quality of life for many. She enjoys expressing her ideas through sketches and illustrations and is actively interested in science communication.
This article was written as part of Club SciWri’s Science Writing Workshop, an initiative aimed at nurturing new voices in science communication and helping participants explore how to make complex ideas accessible to wider audiences.
Workshop conducted by Saurja Dasgupta, Ananya Sen, Rohini Subrahmanyam, Sumbul Jawed Khan and Roopsha Sengupta
