March 06, 2020

Weather Radar Shows Spring Bird Migration

Every day I have been checking the weather radar for signs of the northward migration of our feathered friends, and Wednesday night I finally saw it.

Ornithologists and those tracking the seasonal migration of birds have used weather radar for decades.  The radar signal of a target goes up rapidly with the size of the object (with the sixth power of the diameter) and thus a bird provides an immensely bigger signal than a raindrop.

Many birds like to migrate at night, so a good sign of birds is a large area of radar return that starts around sunset and fades at sunrise.  Meteorological signals don't do that.

And the birds prefer to stay over land--precipitation does not care much about the shoreline.

So let me show you the birds... first at Portland.

At 5:40 PM Wednesday, right before sunset, nothing much was apparent.

By 6:41 PM, within an hour of sunset, echoes were appearing (reddish color), particularly NE of the city.

In the middle of the night at 11:49 PM birds were all over the place!

 Right before sunrise 5:57 AM, the echoes were declining

And gone by 6:59 AM Thursday morning, after sunrise.

National Weather Service radars have Doppler capabilities, which means they can determine the speed of the target towards or away from the radar.  Let's check out the velocities of the birdies (see below). Blue/green means approaching and red/orange means moving away. 

The radar targets are moving to the north---exactly what we would expect for birds migrating northward.

The Hoquiam (Langley Hill) radar showed the birds as well-- here are the radar returns (called reflectivity) at 9:32 PM Wednesday night.  The light blue are birds.  They are not going very far offshore.

So why did the birds decide on Wednesday night to begin moving northward.  Yes, it was the right time of the year...but there is something else.  The meteorology was nearly perfect.

A warm front had moved through the region, followed by strong winds from the south, providing an easy ride!  Plus, the front had virtually no rain. 

To show you this bird conveyor belt, here are the winds above SeaTac Airport for the 24 hours ending 10 AM Thursday.  Time increases to the left and the Y-axis is height in pressure (700-hPa-- is around 10,000 ft). Right after 7 PM Wednesday (05/03), the winds turned strongly southerly (from the south) and stated that way.  Literally, a strong tailwind!

These are meteorologically very smart birds.


  1. The birds have us beat. We make our living in the air but they actually LIVE in the air.

  2. I'm not a birder but thanks for this post Cliff, fascinating....

  3. Thank you - very interesting and exciting. There are so many intelligent systems at play around us. A great opportunity to slow down, take a deep breath, and look up in the sky – albeit with the help of technology.

  4. Fascinating article! Thanks for putting it together.

  5. If you want to see something really amazing, check out this overnight bird migration gif from a few weeks back over Key West. Wow, holy smoke!!

  6. Love this information!

    Thanks Cliff.

  7. Obviously, the saying "bird-brain" is a misnomer... at least for these.

  8. Hey cliff about the allergies, you said on the previous blog that thursday would probably be the worst for allergies, and the rain today would clear things up. However, I felt nothing on thursday and today(friday) I had REALLY, really bad allergies. Maybe the worst I've ever had.

  9. Thanks so very much for that!

  10. Very cool, thanks for the info!

  11. Thanks Cliff. This is brilliant and a welcome distraction from COVID-19 talk!

  12. From "range land" north of Ellensburg (100 miles east of Seattle):
    Each year about this time we have in-migration of eagles looking for a meal as calves come.
    Driving by a couple of ranches this morning we saw many new calves so the kitchen is soon to close. Then the eagles go. Only saw 3 this morning.

    Thanks Cliff.
    We will send a link to some birder friends.

  13. Replies
    1. For posts like this, we want an up-thumb button.

  14. Seems like a dense cloud.. at least the radar makes it look that way. A bird-strike hazard to aircraft?

  15. Excellent! Beginning last week, I heard the birds that overwinter here in California beginning to sing just before they start migrating northward. Once those migratory birds begin singing , they invariably leave here within 2 weeks, not to be heard again in these parts until they return in the fall. Great to see radar confirmation.

  16. Hi Cliff, this is completely off the subject, but I can't find any info on this. Do you know what happened to the WSF Weather website? You featured it in your
    Sunday, March 22, 2009, blog post. Just curious. I used to use it all the time. It just fell off the radar. Thank you for your help.

  17. Great article - thank you! This could be fun to use along the Mississippi River in northern IL. I remember as a kid in NJ, we'd stop our activity for many minutes watching birds head north or south. What website are you using for the radar map? I see something similar, but not exact, on the national weather service site.


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