NASHVILLE, Tenn. (WSMV) – As the seasons change, bird migration begins. Of the many ways to track birds, Doppler radar is one of the most efficient.

It is estimated that over 2 million birds will migrate south every night this week. Some of these birds will fly to the southern United States and others to South America. This migration is tracked year after year.

Birds migrate when the weather gets cooler to find food and nesting sites and to escape the cold. BirdCast is a migration tool that takes into account past migrations, migration patterns and migration timing.

BirdCast also converts weather radar data into information about bird numbers and flight directions to improve understanding of migratory bird movements.

Meteorologists use radars to detect rain, hail, ice, snow, etc. The same radars can also detect non-meteorological targets such as birds and other biological targets.

Dual polarization radars, which we rely on, send out radio waves in both horizontal and vertical directions, allowing the radar to measure the dimensions of targets. Targets like birds are not uniformly sized and are not round like raindrops, allowing the radar to determine that it is not a meteorological object.

In the image above, the green echo you see on the radar is what we know as a “roost ring.” “Roost rings” appear as circular rings on the radar as the beam captures thousands of birds leaving their roosts around dawn.

In addition to birds, radar “interference” can also come from wind turbines, insects and bats, for example. In the case of tornadoes, debris can also be detected on radar.

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