May 02, 2020

Forecasting Bird Migration with Weather Radar and Models

We are now in the midst of the big bird migration time of the year and weather radar can help documents the huge flux of birds overhead.

But even more fascinating, we can skillfully predict bird migration using numerical weather prediction.

One of my favorite sites  to check out bird migration is BirdCast, run by the Cornell Laboratory of Ornithology.  I really appreciate this group and as an undergrad at Cornell I frequently visited their Sapsucker Woods Wildlife Sanctuary.

One of the wonderful things they have on their website is real-time bird migration maps based on the clever use of weather radar (see below).  Turns out that weather radar is a very effective tool for tracking birds, particularly when there is not much precipitation (when the National Weather Radars are in clear air mode).

The map below provides an example:  a real-time snapshot of bird migration at 12:50 AM PDT early this (Saturday) morning.  The colors shows the intensity of bird migration and the orange arrows provide the direction of migration (which can be determined from the Doppler weather radar signal!).  Not surprisingly, most birds are moving northward and the Pacific Northwest is an active migration route.    The largest migration is from Texas to Wisconsin.  By the way, the units of this map is THOUSANDS of bird per km line per hour.   That is a lot of birds!

To confirm the bird invasion, here is the composite radar image the night before (1:38 AM on May 1st).  Wow.  There was very little precipitation that night, so virtually all of this is birds. Keep in mind that there are major gaps in weather coverage (such as east of the Cascade crest).   You note lack of echos offshore...our feathered friends prefer to stay over land!

Our bird friends prefer to fly at night, and the Cornell migration graphic at 9:40 PM Eastern Time yesterday shows this, with the red line indicating the location of sunset at that time.  Very few birds while the sun is up (west of the line), lots of birds to the east of the sunset line.

But this site has even more!  It include forecasts of bird migration activity.    Using decades of radar information to provide migration ground truth, they correlated bird migration activity with forecat weather parameters (from NWS prediction models), day of year, and much more, using a machine learning algorithm. This approach is based on the work of Van Doren and Horton (Science Magazine, 2018) . To illustrate, here is the migration prediction for tonight (Saturday-Sunday), which includes the amount of forecast precipitation as well.

Less birds tonight..and that has to do with the change in the weather.   This bird forecast research noted above (Van Doren and Horton) found the bird migration correlates best with temperature (more migration with warmer temperatures), with precipitation also discouraging our feathered friends.  The strong front moving through today will result in both cooler temperatures and showers.  Thus, our migrating bird visitors will take a well deserved rest this evening.

Finally, I should mention that there is all kinds of fascinating information in that Van Doren an Horton papers, such as the annual variation in bird migration over the U.S. based on the weather radar data (see below).  Peak migration is in early-May, with a huge ramp-up in we are very near the peak now.  Thus, watching the radar now is of particular interest for all bird lovers.
So during the next mild night this month, look up and imagine the thousands of birds that are moving northward above your head.  Kind of reassuring during these difficult times.


  1. Would prefer to see your take on the supposedly tumultuous weather we are being told to experience these next 48 hours...birds gonna fly !

  2. Isn't it amazing! Isn't it amazing! I am humbled by my grandparents...dedicated "birders" who (decades ago) spent their retirement years following/documenting bird migrations from Mexico to Canada with other likeminded individuals.

  3. I'm amazed that with this many birds in the air there aren't more collisions with aircraft. Do the airline ops people look at this and alter routes around the densest areas? Or is it that, even with all these birds, the airspace is still almost entirely empty?

  4. Wow! I wonder what altitudes these birds are flying at. Lower 1,000 ft? Up to 5,000? Fascinating.

  5. Cliff,

    I find bird migration fascinating and am happy to see you featuring their movements in your blog. I knew and worked with wildlife scientists who specialized in bird migration. Nature is so interesting and yes it is reassuring to revisit the natural rhythms still in place as we are somewhat displaced with our own rhythms.

    I should have remembered that your work overlaps with bird migration. Thanks for the reminder.

  6. Good post Cliff. I'm going to bookmark BirdCast to keep track. Migration had often been estimated via bird banding stations. But a change in the weather could push the birds east or west on different years making abundance estimates unreliable. Combining radar and weather will be more reliable by providing a more extensive view.

    A 2019 paper suggesting 2.9 million fewer birds since 1930, also used radar to estimate migrating bird biomass suggesting birds had declined over the eastern flyway but not the central and western flyways. . It is interesting to see the dramatic difference in birds between May 1 and 3rd on your maps along the eastern flyway. An analysis comparing their data and weather needs to be done. I analyzed their paper and they were too eager to push unjustified bird doom

    My analysis was blogged as Hopefulness Despite 2.9 Billion Lost Birds.


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