NEXRAD radar used to predict bird collisions

The overnight migration activity of native bird species, such as the brown thrasher, is visible on weather radar and correlates with bird deaths that occur from building and window collisions.

STILLWATER, Okla. – Oklahomans are familiar with tornado warnings, but what about bird warnings? New research conducted by Oklahoma State University scientists and published in the “Journal of Applied Ecology” indicates weather radars are effective tools for not only predicting weather but also bird collisions. 

As many as 1 billion birds die each year from colliding with windows or buildings, but the casualties are not those of pigeons or other invasive species most commonly found in urban areas. Instead, the victims are native species—a diverse array of species in the North American avifauna, such as warblers, thrushes, hummingbirds, sparrows and orioles, that fly into structures during their spring or fall migrations. Declining populations of native birds are cause for alarm to many bird conservationists who are searching for ways to prevent these fatalities. 

“A lot of the birds that collide are nocturnal migrants that fly primarily at night because they’re so small and have such a high metabolism that they’d overheat in the daytime,” said Scott Loss, an OSU associate professor of natural resource ecology and management. “The effects of light pollution in cities and around tall buildings can attract and confuse these migrating birds, causing them to collide.” 

Overnight, large numbers of birds travel using the stars and other orientation cues, such as sensing the Earth’s magnetic field, but buildings and other tall structures can be difficult to identify. This is especially true for the attractive and disorienting power of light pollution coupled with the disorienting and deadly effects of window glass. Loss has studied bird collisions extensively for the past several years, and this new investigation, supported by OSU Ag Research, is the first to involve a weather radar system. Birds fly high enough in the atmosphere and in large enough flocks that their activity is detected by radar beams intended for tracking aircraft, precipitation and storms. 

“It’s not as crazy as it sounds. Radars have been used to study bird migration for more than 50 years,” Loss said. “Migrating birds look different than rain and storms. Most meteorologists have a way to turn off that ‘clutter’ and filter it out to focus on precipitation, but biologists have learned they can do the opposite.” 

When the precipitation and weather are filtered out, scientists can use radar technology to monitor dust, insects and birds. As a doctoral student in the Department of Natural Resource Ecology and Management from 2016 to 2020, Jared Elmore monitored bird activity on NEXRAD radar available to the public from the National Weather Service. Now a research associate at Mississippi State University, Elmore’s dissertation focused on several bird conservation issues. As a participant in the Knopf Doctoral Fellowship Program in Avian Ecology and Conservation, he targeted Stillwater by collecting data from radar sites near Enid, Tulsa and Oklahoma City. 

“We wanted to take a new spin on studying bird collisions. I downloaded the radar files through Amazon Cloud Services and learned how to code to identify the bird signatures on screen,” Elmore said.

Elmore’s radar data then was aligned with bird carcass counts documented by doctoral student Corey Riding and associate professor Tim O’Connell. For two years, April through October, Riding conducted daily surveys at 16 designated buildings on the OSU campus and in Stillwater. 

“I’m interested in the urban ecology of birds and how they interact with manmade environments,” said Riding, who currently teaches biology at Salt Lake Community College. “Studying collisions is important because it’s such a large mortality source for these birds.” 

Other co-authors outside of OSU included Kyle Horton of Colorado State University and Andrew Farnsworth of Cornell University. Both are international leaders in using radar images to study and predict bird migration patterns. 

“The analytical approaches developed by our collaborators, such as the method to filter out objects that were unlikely to be birds, were crucial to the research,” Loss said. 

The birds detected on night radar scans directly correlated with collision fatalities Riding observed in Stillwater the next morning. 

“We can calculate the migration traffic rate by estimating the number of birds that are crossing an imaginary line over the course of a night,” Loss said. “The nights with heavy migration traffic on radar resulted in more bird collision victims found at daybreak.” 

The weather radar marvel of bird collision research was featured in the March issue of “Discover Magazine,” and the group plans to share their findings with conservationists nationwide. Loss and Farnsworth also are working together on a bird-window collision project known as Lights Out Texas. A coalition of conservation nonprofits, universities and governmental organizations that partner with homeowners, building managers and municipal leaders, Lights Out Texas aims to reduce light pollution and bird collisions in the downtown districts of major Texas cities. From 11 p.m. to 6 a.m. each night through the spring migratory season of March 1 to June 15, Texans are advised to turn off or dim their lights. Volunteer scientists in each city will monitor bird-window collisions during the spring 2021 migration. Other U.S. cities such as Chicago have dimmed downtown lighting during spring and fall migrations since the early 2000s.

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