Singing Overtime 

Artificial light from homes and streetlights helps people prolong their days.   

For birds, however, it means working overtime.  

That’s the conclusion of a new study that found that city birds are singing earlier in the morning and finishing up later in the evenings in areas with more artificial light. 

“We were shocked by our findings,” study author Brent Pease told the Guardian. “Under the brightest night skies, a bird’s day is extended by nearly an hour.” 

Researchers used recordings submitted by bird enthusiasts to a popular species identification and mapping website called BirdWeather, wrote Smithsonian Magazine.  

They analyzed 2.6 million morning calls and 1.8 million evening calls from more than 500 bird species and compared the findings with the light pollution levels measured by satellites. They found that birds in places with higher light pollution started their days about 18 minutes earlier in the morning and stopped singing about 32 minutes later at night. 

“For these birds, effectively their day is almost an hour longer,” study author Neil Gilbert told NPR. “They start vocalizing about 20 minutes earlier in the morning, and they stop vocalizing about 30 minutes later in the evening.” 

The study also found that some species, especially those with larger eyes compared with their body size, are more impacted by light pollution than others. 

“The American robin, Northern mockingbird, and European goldfinch all extended their day by more than average,” Pease told the Guardian. “Small-eyed species such as sparrows didn’t have as much of a response.” 

So far, it is not clear how longer days impact birds. 

“We know that sleep loss is not great for humans, but birds are different,” said Pease. “They have developed interesting strategies to cope with loss of sleep during migratory periods.” 

While researchers were concerned about disruptions of natural behaviors, Pease noted that, in some species, artificial lighting can extend foraging and mating time and boost the survival rate of fledglings. 

Scientists already knew that light pollution affects birds and other animals. For example, it can confuse sea turtle hatchlings trying to reach the ocean.   

This study, however, is the first to analyze this phenomenon across hundreds of bird species on multiple continents and during different seasons, providing researchers with unprecedented insight into how artificial light affects the lives of birds worldwide.