April 13, 2012

Bird Migration on the Coastal Radar

I have mentioned before that we often see birds at night when the radar is in clear-air mode--the highly sensitive setting that is used when there is not a lot of precipitation around.  In fact, there is a whole discipline centered around this tool:  radar ornithology.

Well, we have our new coastal radar and I was wondering how the birds look from a  coastal perspective and particularly whether our feathered friends like to fly offshore.  Lets get some answers!

Here is the composite radar image a little after sunset, when there was still plenty of light in the sky (8:33 PM, Thursday).  A few echos, with a lot of ground clutter around the radar (radar beam hitting the surface).

 One hour later, a lot of red/orange echoes--those are the birds.

 An hour later...even more birds.  Interestingly the birds don't seem to fly very far offshore (the few isolated echos you see over the Pacific are some light showers).  Perhaps someone can tell us why.

Still doubt they are birds?   Well, we can check the direction of motion using the Doppler radar capabilities of our radar, telling us the speed of the "targets" towards or away from the radar. Green indicates flow towards the radar and red away...and the velocities are quite substantial (up to around 30 kts).  The color indicates that these objects are moving northward..what we would expect from spring migration.  The birds had a tailwind last night (literally!) since there was southerly flow in the lower atmosphere.

 These bird echoes disappeared around sunrise....something that is clearly not meteorological.

The sun is long set tonight (Friday) and here is the latest radar image from Langley.  Same deal...lots of birds.   Note the appendage sticking out near Grays Harbor...that is sea clutter....the radar beam is hitting the ocean surface and reflected back to the radar.  There was some worry that our new radar might have a more serious sea clutter problem, but as you see it is a minor issue.

Tonight the winds are from the north aloft and the Doppler velocities are weaker but still indicate targets that are moving north (see image), but at a slower speed.  The reason:  tonight our feathered friends have a head wind slowing their progress!

If only birds could interpret weather radar imagery....

Preparing for tonight's migration


  1. Looks like I get to look forward to some of my Washington state friends and family talk about birds in the weeks to come.

  2. Ah, love the bird cartoon! :)

  3. Very interesting!

    As a pilot, that color density from birds is a bit scary. Maybe in the future using radar systems to track bird flocks will be more commonplace, and we can improve safety for both birds and aviators.

  4. Cliff, can you tell from the doppler returns how high the nocturnal migrations are?

  5. Your blog on bird migration is just another reason why you are my #1 favorite weather man! I've just sent the link to my birder friend in Australia.
    Thanks for your work.

  6. When I did a stint at the Bermuda Biological Station in, umm...1979, I think -- I was told that the Navy radar on Bermuda was the first hard evidence that North American songbirds migrate way the hell out to sea, in both migrations (Spring northward, and Fall southward). Sure, there had been the occasional "fallout" of songbirds on the storm-vex'd Bermoothes before that, but it was assumed they were lost birds: nobody could believe they could migrate that far in one fell swoop (as it were). Cheers!

  7. Radar ornithology is intriguing. Is it possible to tell more about the birds from their radar returns? I'm thinking about how the radar can show rain, snow and mixed rain/snow. The ability to discriminate types of precipitation makes me wonder if it's possible to use radar to tell more about the size, shape, or species of flocks or perhaps even individual birds?

  8. I remember learning this is skywarn radar classes! So weird!

    Caleb Chapman

  9. http://www.tpwd.state.tx.us/huntwild/wild/birding/migration/faq/ says "Migration over water is one of the most hazardous times for birds, especially small songbirds. Millions of migrating birds perish at sea. These are often young birds or birds that are blown off-shore or forced down by bad weather." Birds that fly over land have many more options for shelter and food.

    "Predicting Birding Conditions With Radar" at
    has links at the bottom to many regional websites that include radar interpretation and/or provide migration forecasts.

    Maybe you should be listed there too? Many thanks for your posts!

  10. What's the range of the radar? Trying to understand if the boundaries of the bright orange area represent the boundaries of the flock or just the range of the radar.


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