Between March and June 2024, areas across the United States will experience the highest aerial bird density of the year. In other words, the period from late spring to early summer is considered ‘peak bird migration’ season in the United States.
Since 1999, a collaborative research group called BirdCast, made up of scientists from the Cornell Lab of Ornithology, Colorado State University, and the University of Massachusetts Amherst, has been using radar tools to monitor nightly bird migration across the United States. BirdCast defines ‘peak migration’ as the period of time ‘when the nightly average of birds in the night sky was highest – as measured by 143 radar systems from coast to coast, with each radar measuring aerial bird densities every 10 minutes from 2013 to 2022’ (Axelson and Leonard, 2024). During such times, over a billion birds could be in flight on a given night.
While bird migration is an amazing sight to behold, it’s also a dangerous time for birds who must migrate through urban areas, as the light emitted from skyscrapers and other buildings in urban environments can be confusing and disorienting. According to the Cornell Lab of Ornithology, within the United States, approximately 600 million birds are killed each year from collisions with skyscrapers (Dapcevitch, 2019). In particular, Chicago, Illinois; Houston, Texas; and Dallas, Texas, rank among the most dangerous cities in the United States for migrating birds (Dapcevitch, 2019).
Light pollution has even greater implications during spring and fall migrations, when billions of bird species migrate between North and South America. Migrating birds rely on natural light from celestial sources such as the sun, moon and stars in order to navigate. Artificial light pollution negatively impacts this process. In North America, for instance, there are four main flyways, or ‘avian superhighways’, which are generally understood to be the Atlantic, Mississippi, Central and Pacific Flyways (Fritts, 2022). When migrating cross-country, birds seek out efficient pathways with ample places to rest. Some bird species stay closer to coastal areas, while others prefer inland paths or follow larger rivers or mountain ranges. For birds to successfully migrate, however, they require navigable flyways, and light pollution is highly detrimental to this process.
These migration routes, or flyways, are also referred to as aerial corridors.
Aerial corridors are an emerging area of research for corridor ecology and wildlife connectivity, and light pollution is one of the main disruptors for wildlife, especially birds, who must migrate through corridors in regions prone to light pollution.
Organizations like the National Audubon Society are trying to mitigate this issue with ‘Lights Out’ programs designed to educate citizens about ways to reduce energy consumption by keeping lights off strategically during certain times when bird species are migrating through urban areas. By lessening light pollution at strategic times, we can help migratory birds more easily get to where they’re going. But there are other benefits for people, too; it’s been documented that reducing light pollution has considerable economic benefits in addition to protecting migratory birds.
I discuss this nascent topic of aerial corridors in more detail in my new book, An Interdisciplinary Approach to the Theory and Practice of Wildlife Corridors: Conservation, Compassion and Connectivity, forthcoming with Anthem Press in June 2024. The book not only provides much of the knowledge necessary for a general and credible understanding of connectivity projects, but also makes a unique theoretical contribution to current knowledge about wildlife corridors by arguing that theories about compassion, empathy and traditional ecological knowledge should inform wildlife corridor projects.
References
Axelson, Gustave and Pat Leonard. ‘When Will Spring Bird Migration Hit Its Peak? BirdCast Has Answers’. All About Birds, 26 April 2024. Web. 22 May 2024. https://www.allaboutbirds.org/news/when-will-spring-bird-migration-hit-its-peak-birdcast-has-answers/#.
Dapcevitch, Madison. ‘American Skyscrapers Kill an Estimated 600 Million Migratory Birds Each Year’. EcoWatch: Environmental News for a Healthier Planet and Life, 10 April 2019. Web. 21 May 2020. https://www.ecowatch.com/birds-killed-skyscrapers-light-pollution-2634222993.html.
Fritts, Rachel. ‘Avian Superhighways: The Four Flyways of North America’. American Bird Conservancy, 16 May 2022. Web. 31 Aug. 2023. https://abcbirds.org/blog/north-american-bird-flyways/.