Thursday, October 30, 2014

Fall Bird Migration Caught on Weather Radar

On Tuesday evening I noticed some peculiar radar returns developing on the Lincoln IL radar beginning about 6:45 p.m. CDT. The returns appeared to develop along the Illinois River, and my first thought was that it might be biological. I checked the satellite image for the region and there were a band of clouds over central Illinois, so I attributed it to precip, even though none was expected.

While working in my home office last night I glanced at the radar and similar returns were starting to show on the radar at the same time as the night before!. For a moment I thought that perhaps I was looking at an image from the previous night. The returns developed along the Illinois River, and then moved to the southeast. After some inquiries of friends and colleagues, it appears what we were seeing on radar was the fall migration of thousands of birds, probably mostly waterfowl. The birds took flight about 50 minutes after sunset.

Lincoln, IL radar images for Wednesday night, October 29.
Tuesday, October 28. Click on image to view a two hour loop of the radar.

Reports and forecasts of fall migration are available on BirdCast, part of the Cornell University Lab of Ornithology web site. Regarding the migration through the central U.S. on Wednesday BirdCast indicated that

"This night will surely represent one of the last large movements of the fall of both landbirds and waterbirds. Species on the move this week will include Hooded Merganser, American Tree Sparrow, Lesser Scaup, Common Loon, Red-breasted Merganser, Lapland Longspur, Canvasback, Bonaparte’s Gull, Fox Sparrow, Greater Scaup, Ring-necked Duck, Common Goldeneye, Redhead, Dark-eyed Junco, and Ruddy Duck."

Credit: U.S. Fish & Wildlife Service
A colleague of mine who is a birder reported that he had seen a report of thousands of waterfowl at Chautauqua National Wildlife refuge near Havana on the Illinois River. There are other National Wildlife Refuges along the Illinois River as well.

The Illinois River is a major flyway for migratory birds and the most striking radar images I found came out of Lincoln. However, birds taking flight were also captured by the Des Moines, IA and Kansas City, MO radars on Tuesday night.

Des Moines, IA radar at 7:11 p.m. CDT Tuesday, October 28. The dark blue and green returns are likely birds taking flight.
Kansas City, MO radar at 7:27 p.m. Tuesday, October 28. Note how the bird returns are along the Missouri River.

Birds use a variety of means to navigate during migration, including the sun, stars, and magnetic fields. It is thought that nighttime migration is advantageous for birds because of the lower temperature. Birds generate a lot of heat while flying, and lower temperatures (and lack of sun) help them maintain and optimum body temperature as they travel.

You can learn much more about bird migration at the following web sites:

Northern Prairie Wildlife Research Center
Cornell University Lab of Ornithology  

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