Nexrad Ornithology

By now most birders have heard about Nexrad (Next-Generation Radar) and how it can be used as a tool to view and track nocturnal bird migration. During spring and fall migration, I use Nexrad as an indicator of how “good” the birding might be the following morning in terms of numbers of individuals. However, keep in mind that a lack of Nexrad activity doesn’t necessarily mean birding will be slow the next morning. Inclement weather may keep birds from migrating, so the woods might still be filled with neotropical migrants from the previous day.

Amateur and professional ornithologists use Nexrad to track migratory birds. Density estimations give ornithologists the ability to count the number of birds involved in migratory movements, specific direction routes, timing, speed, elevation, and correlation with weather patterns. Birds can detect storms by sight, smell, sound, humidity, and pressure, and often attempt to fly around the storm cell, reverse direction, or are forced to land. All of this can be detected and viewed live on Nexrad. My favorite online Nexrad website is the National Center for Atmospheric Research/Research Applications Program - Real-time Weather Data or NCAR/RAP.

To see live Nexrad maps, I change the “Product” to “Regional Reflectivity” and leave the “Background” set to the default “black” option. For a quick snapshot, I leave the “Loop Duration” set to “Single image.” At this point you can either click on an individual radar station (three-letter codes across the states), or to see an entire map of US Nexrad data, select “Contiguous U.S.” at the top.

How do you tell the difference between migrating birds and storm systems on Nexrad? The precipitation density of a storm is higher, so they often appear as massive, spinning, amoeba-like shapes. Because of how radar works, and the comparatively even distribution and lower density of flocks, birds show up as concentrated, circular donut shapes centered on a radar station. The gaps between the donuts are just an indicator of the Nexrad station’s range for that density. Migratory birds are still present in those gaps.

Nexrad can be a fairly useful prognosticator of expectation when combined with phenological knowledge of arrivals and departures of birds. Spring migration is nearly upon us. Soon our backyards and local natural areas will be filled with the songs sung by colorful birds. Studying Nexrad maps doesn’t really compare to the undiluted joy of birdwatching, but as an adjunct to the pasttime, viewing actual bird migration on a macro scale certainly enhances one’s appreciation of the phenomenon.

Article contributed by Mike McDowell, an avid digiscoper, amateur naturalist, and Eagle Optics employee.

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