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A new study is underway to characterize the risks to migratory birds as they travel north from Central and South America and the Caribbean in the spring and south in the fall.
Jin Bai, a graduate student at North Carolina State University, studies factors that could increase the risk of bird collisions with windows, especially for migratory birds, since collisions are one of the leading human-related causes of bird mortality in North America.
The Summary spoke with Bai about why the birds make this journey each year, as well as his work studying risk factors for bird-window collisions. Bai led the study with Madhusudan Kathi, associate professor of forestry and environmental resources at NC State.
Summary: When do birds migrate?
Bai: Most birds migrate in spring and autumn. Spring migration in North Carolina begins in late March, peaks around late April, and begins to slow down by late May. The autumn migration is relatively longer, from August to October. You can use BirdCast to see estimates of how many birds are flying overhead in your area.
TA: Why do they migrate?
Bai: This is evolutionary behavior. By migrating north in the spring, they migrate from low-resource areas to high-resource areas for food and nesting sites.
TA: What are some of the risks to birds as they migrate?
Bai: Collision between birds and windows is a big threat to birds. Researchers estimated in a study published in 2014 that about 988 million birds are killed by building collisions in the United States each year. A study in the Triangle area a few years ago found that migrating birds may be more vulnerable to collisions with buildings. Native birds may be more familiar with their environment.
Fall migration has more collisions for several reasons. One reason is that many birds have finished breeding in the fall. Young birds are less experienced. Also, there are more birds migrating in the fall than in the spring because the fall migration includes both adults and juveniles, while the spring migration includes only adults.
TA: Is there anything that shows what they tend to run into and why?
Bai: There are several factors. They migrate at night and use stars for navigation. When there is light pollution, it disorients them. Also, they may stay around an urbanized area that they may have avoided without the lights, where there are lots of windows. They see the reflected trees or sky in the windows and think they can fly through them; that’s why they clash. So the light disproportionately attracts birds to the city, and then reflective materials can cause collisions.
TA: What can people do to help?
Bai: People can help by turning off lights during migration periods and by putting up window film. Some of the window films have a pattern of dots that can help prevent bird collisions. These films can have different dot patterns that are of different shapes and can be transparent, white, black or UV coated. The American Bird Conservancy is a non-profit organization dedicated to the conservation of wild birds and their habitats across America; they have a whole database of effective window treatment products. There are also solutions at the political level. In some larger cities, there have been efforts to change window codes in new buildings, and some cities in North Carolina are campaigning to turn off lights during the migration period.
TA: What is your research in this area?
Bye: I lead a bird strike tracking study at three institutions of higher education: the University of North Carolina at Chapel Hill, Meredith College, and NC State. The main objective is to identify high-risk buildings and advocate solutions for these buildings. The other side is to contribute to the science of bird window collisions to know how building characteristics or other factors such as migration intensity or weather may be related to collisions.