Blue Light Exposure Raises Collision Risks for Migratory Birds in Urban Settings

by | Apr 17, 2024

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Bird collisions with buildings are a longstanding issue, exacerbated by urban lighting—mainly blue light, which has now been identified as a significant risk factor for nocturnal migratory birds. A study by University of New Mexico scientists David Tan and Nicholas Freymueller, published in Conservation Biology, provides new insights into the interaction between urban light pollution and bird migration paths.

A New Perspective on an Age-Old Problem

Birds crashing into buildings isn’t just a local problem; it’s a worldwide concern. In North America alone, it’s estimated that between 365 million and 988 million birds die each year from hitting buildings, with migratory birds being the most affected. Surprisingly, there’s been little research on this issue in tropical regions like Asia and Africa, so we don’t know much about how or why these collisions occur there.

Most studies on bird-building collisions have focused on just a few buildings, typically in city centers or university campuses. These studies show that prominent, glassier buildings with more light are more dangerous to birds, but it needs to be clarified if this is true for all parts of big cities.

This study, conducted in Singapore used ecological niche modeling to predict collision hotspots across the island. Typically used to determine living habitats, the researchers adapted the method to define where birds most likely encounter deadly obstacles. Their findings indicate that buildings emitting high levels of blue light at night are particularly dangerous for migrating birds, known for their vulnerability to light during nocturnal migrations.

David Tan, a Ph.D. candidate at the University of New Mexico’s Department of Biology, took a different approach in his Singapore-based study. Rather than looking at a few buildings, he and Freymueller gathered data on dead birds from all over Singapore, a densely populated area slightly smaller than New York City but with over 100,000 buildings. They used a technique called ecological niche modeling to predict where animals live and determine where birds are most likely to die from hitting buildings. This method considers how environmental factors like weather patterns might influence where these fatal collisions happen.

With help from other local universities, the team analyzed records of bird collisions from 2013 to 2020. They found that migratory birds called pittas, which are very colorful yet secretive, are particularly prone to dying from building strikes, especially in areas with blue light pollution. This finding is crucial because it shows that switching to white LED lights, which save energy but emit a lot of blue light, could make things worse for these birds.

The study also discovered that non-migratory birds, like green pigeons and emerald doves, often hit buildings on the edges of forests. This might be because they travel through cities, moving between patches of forest. Based on these insights, the researchers identified future building projects in Singapore that are likely to see more bird collisions, particularly those close to forests and bright lights.

Tan pointed out a unique advantage in Singapore: the government’s detailed and advanced planning helps predict where problems like bird collisions might happen. This foresight allows urban planners and developers to include bird-friendly features in new buildings, like special glass that birds can see more easily, to prevent these accidents before they happen.

Implementing Solutions

The implications are clear: urban centers globally need to reassess the impact of their lighting on wildlife, especially birds that migrate by night. While energy-efficient, the move towards white LED lighting, poses an increased threat to these species due to its significant blue light component.

The researchers suggest several mitigation strategies for urban planning and building design. Bird-safe glass, mullions, and louvers are recommended for areas identified as high-risk, particularly near forest edges and in regions marked by extensive blue light pollution. By shifting to lights with warmer color tones and using directional shielding to prevent light spillage into the sky, cities can help reduce the number of migratory bird deaths.

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