Is Weather Radar for the Birds?

Radar is designed to detect "things" in the air. In meteorology those "things" are hydrometeors - rain drops, ice crystals, hail, and even clouds.   However, for a long time radar has been recognized as a tool to detect birds and insects in the atmosphere.

In the last couple of weeks there have been two cases where weather radar has captured bird and insect movement. The first of these was the detection of a massive mayfly emergence along the Mississippi River on July 20. This event received a lot of media coverage because of the size of the emergence and the photos of the swarms of mayflys. The mayfly emergence and its northward drift was detected by radar throughout the evening. By late evening reports were coming of the piles of mayflys in communities near the river.

Radar loop of mayfly emergence on July 20 along the Mississippi River.
The loop is for the period from 8:35 p.m. to about midnight CDT

The photo below was taken by Tim Halbach, a forecaster at the NWS La Crosse office and a CoCoRaHS observer, a little after midnight on July 21 several hours after the beginning of the hatch.  Tim decided to go out "mayfly chasing" after his shift ended at midnight.

Photo taken at 12:15 a.m. on July 21of mayflys covering the building and pavement.
Photo by Tim Halbach

Mayflys spend the better part of the year as aquatic nymphs in the mud. During the summer they emerge as adults to find a mate. While this year's major event on July 20 got a lot of attention, mayfly emergence occurs every year along the river.  It's not always this massive, or this gross.  The NWS La Crosse office has a page on its web site dedicated to the mayfly emergence events in that area.It includes radar images and many photos submitted by residents of the area.

You can read more about the program to monitor mayfly emergence at the U.S. Fish and Wildlife Service web site.


Another interesting although less spectacular detection by weather radar was that of a "roost ring" Tuesday morning by the Chicago weather radar. A roost ring is radar signature of birds as they leave their morning roosting site. This one occurred about 5:30 a.m. along the Kankakee River in northwestern Indiana.

A roost ring detected the NWS Chicago radar at 5:30 a.m. CDT on July 29.

Roost rings are typically seen in late summer and early fall leading up to fall migration when birds gather at large roosting sites. The rings occur when the birds take flight in the morning. Roost rings are typically seen in the morning when atmospheric conditions are favorable for the birds to be detected by radar. Often there is an inversion (a layer where temperature increases with height), and that has the effect of bending the radar beam back toward the earth and is more likely to detect objects close to the earth's surface..

The NWS Wilmington, OH office has a nice description of the occurrence of roost rings along with some radar images.   

 If you would like to read more about the use of radar in detecting birds and insects, check out Radar Technology - A Tool for Understanding Migratory “Aerofauna”   by the U.S. Geological Survey.