How Unnatural Light and Noise Affect Birds

Light and noise pollution often have an impact on reproductive success.

Male Northern Cardinal (Cardinalis cardinalis)
The northern cardinal has a relatively low frequency song and delayed breeding in response to noise pollution. Kryssia Campos / Getty Images

We know light pollution and noise pollution can threaten the health and well-being of humans, animals, and the environment. Researchers have long studied the impact on birds and how an overabundance of brightness and sound can impact their breeding, feeding, and migration behaviors.

A new study, published in Nature, takes a comprehensive look at how noise and light pollution affects birds throughout North America. It found that these factors can affect how birds succeed and often are intertwined with the impacts of climate change.

“We wanted to do this study because much of the existing literature on the effects of noise and light have not only been mixed in terms of whether impacts are negative or positive, but also have focused on responses that don’t tell us whether these stimuli have consequences that could influence populations,” Clint Francis, a biologist at California Polytechnic State University and one of the lead study authors, tells Treehugger.

Francis points out that knowing that a bird changes its song because of noise doesn’t explain whether noise pollution influenced the bird’s fitness or reproductive efforts.

“Similarly, whether light alters hormone levels in birds does not tell us whether these are coping mechanisms that allow the animals to succeed under challenging conditions or whether it is indicative of bigger problems for survival,” he says.

Recent research finds that the number of birds in the U.S. and Canada has plummeted over the past 50 years, dropping by 29%, according to a 2019 study published in Science. That's a decrease of 2.9 billion birds since 1970.

Keeping Up with Climate Change

For the study, researchers looked at data collected by other researchers and by citizen scientists. They analyzed how light and noise pollution affected the reproductive success of more than 58,000 nests from 142 bird species across North America. They considered several factors including the time of year when breeding occurred and whether at least one chick fledged from the nests.

Birds typically breed about the same time each year, using daylight cues to time their reproduction to coincide with when the most food will be available to feed their babies. 

“Artificially changing day length with light pollution essentially misleads them to start breeding earlier than they normally would,” Francis says.

When that happens, sometimes chicks hatch before food is available. But with climate change, sometimes the results are a little different. 

“We also found that the same species that breed earlier appear to benefit from light exposure in terms of nest success. This was unexpected. We do not know for sure that light pollution helps birds cope with climate change, it needs to be tested in further research. Nevertheless, it is quite possible that light allows birds to ‘catch up’ to earlier prey availability due to climate change,” Francis explains.

Researchers know through studies of climate change that plants and insects are starting to emerge earlier each spring. They respond to warmer temperatures rather than light. So possibly the birds are benefiting from that change.

“A likely explanation is that light pollution causes birds to nest earlier and restore the match between the timing of their nesting and the highest availability of their food,” Francis says. “Again, this needs to be tested. Still, if true, it means that birds exposed to light pollution are ‘keeping up’ with climate change and those in pristine areas where there is no light pollution would not.”

Responding to Noise Pollution

When it comes to sound, researchers found that birds in wooded areas were more affected by noise pollution than those in the open.

Birds in forested environments typically vocalize at lower frequencies because these signals are better able to travel farther through dense vegetation, Francis says.

“Not only did forest birds lay fewer eggs and have lower nest success with increased noise exposure, we also find that birds that have the strongest delays in nesting due to noise are those with the lowest frequency song,” he says.

Why are noise pollution and vocalization linked?

“Well, human-made noise is very low in frequency and thus has a stronger potential to mask or ‘cover up’ birds with low frequency versus higher frequency songs and calls,” he says.

The study findings can have key implications for conservation efforts in urban and non-urban areas, researchers say. Limiting noise and light pollution can help increase birds’ success.

“We should do as much as we can to restore natural sound levels and lighting at night,” Francis suggests. “Unnecessary noise and light should be eliminated or minimized. Quiet road surfaces, use of more electric vehicles and use of vegetation and berms near roads could drastically reduce noise pollution. For lights, use of smart lighting technologies that only turn on when needed by a person would help restore natural darkness.”