Every spring and fall migration a big deal is made of using weather radars to track migrating song birds. But how much can we really read into this?
First off, the radars usually have to be in what is called ‘clear air mode’ the most sensitive of radar modes. This usually happens on clear, dry nights. The radar uses 5 different elevation scans to try and pick up the slightest precipitation. This mode however also picks up anything flying and not flying in the air, including birds, but also bats, airplanes, insects and mountains. Dust and smoke also can be picked up as well.
But how much of what we see on radar should we believe? If you look at Key West, FL there is no land elevation, thus in theory anything over 100′ is likely flying. Thus heavy radar returns on dry nights during migration are likely migrating birds. But also look at Albany, NY. The elevation of the city is only 197′ above sea level, but in the area that the radar scans land elevation goes up to nearly 5,000 feet. Thus the lower scans of the radar often pick up trees, mountains and other objects, giving false returns. The radar does pick up birds, but you won’t be able to pick them out unless they are above 5,000 feet. Anything below that is unclear. It also takes some practice and a little bit of skill to accurately read weather radars.
Radar should only be used as a guide. There are times when radar can pick up migrating birds well and this can translate to forecasting a fall out in a particular location. But they can also be misleading. So the next time you look at your local radar on a clear, dry Spring or Fall night and see heavy returns, remember to be cautious, especially if you have any elevation… But still get out at dawn, just in case.