Bird-dar? Watch migration using weather radar.

Updated: Oct 11, 2020

Did you know large movements of birds and other flying animals are captured each year on radar?

Live Migration Map
Bird migration captured on radar in early September around midnight.

How many birds migrate in North America?

Each year in North America, several BILLION birds migrate north in spring and south in the fall. How are these numbers determined? Scientists use a tool originally designed for tracking weather events, radar. Utilizing 143 weather stations across the United States, Cornell Lab of Ornithology researchers determined that over 4 billion birds depart the US for Latin America each fall. In the spring, 3.5 billion birds return to the United States.

We've discovered that each autumn, an average of 4 billion birds move south from Canada into the U.S. At the same time, another 4.7 billion birds leave the U.S. over the southern border, heading to the tropics,” noted lead author Adriaan Dokter, an Edward W. Rose postdoctoral fellow at the Cornell Lab. “In the spring, 3.5 billion birds cross back into the U.S. from points south, and 2.6 billion birds return to Canada across the northern U.S. border.

How to read a radar map for bird migration?

Bird Migration occurring in early September
Bird Migration occurring in early September

When looking at a radar map, look first for the obvious storms. These are usually oddly shaped and moving from west to east. Next, look for the "biological blooms" or round radar blobs appearing across the map. These blobs usually only begin to appear after sunset at their respective location. There have been instances of meteorologists blowing these blooms off as anomalies, raising the ire of birdwatchers! It even lead to an embarrassing moment for a meteorologist unaware of the extensive studies into bird migration radar. (That poor person had to issue several apologies and retractions.)

Here's what each circle on the image above means:

Red - this biological bloom is likely made from birds. The blooms are not always circular, as is the case in the Rockies near Denver, CO.

Green - These are storm systems showing the asymmetrical shape and moving from west to east.

Yellow - This LARGE bloom is likely a combination of birds, insects, and A LOT of bats!

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Want to learn more about bird migration?

Check out Sibley's "What It's Like to Be a Bird (Amazon)."

How to use radar to maximize your birdwatching experience?

Using eBird data and the live maps below, you can determine which birds are moving to and from your birding region. This helps some birders find rare species that are pushed off their typical migration course due to winds and storms.

To maximize your experience, follow these steps:

  • Go to

  • Click the 'Explore' tab

  • Select bar charts

  • Select a region or location

  • Use the bar charts to determine arrival and departure of listed species

  • Or click on the Line Graphs icon next to the species name

  • Compare these dates to current migration events shown on the live maps listed below

Learn when large flocks of birds move, like this Snow Goose flock.
Learn when large flocks of birds move, like this Snow Goose flock.

How radar is used for bird conservation?

Nocturnal collisions with buildings is a major hurdle for migratory bird species. There are instances of 500+ birds being killed in a few hours by a single building that failed to turn out its lights during migration events. While shutting out lights every night may not be plausible, researchers have combined radar science, migration statistics, and citizen science data to determine when and where lights need to be out.

CSU and CLO have been able to predict high bird traffic areas and the potential light pollution areas they may encounter. A combination of heavy light pollution and high bird traffic create a 'high alert lights out warning.' This alerts local governments and property owners that shutting off lights can prevent catastrophic bird kills.

Live Migration Radar for the United States

These maps are from the Cornell Lab of Ornithology and NOAA. BirdCast interprets the radar information so you do not have to. In fact, they even tell you the direction the birds are moving and how many are moving. It is the best tool for watching bird migration radar.

This map from NOAA & the NWS is a live map of radar activity in the United States.

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