Tuesday, September 06, 2011

Warbler Migration and Nexrad!

Nashville Warbler

What's been going on? Lots of birding, of course! Though it seems to me like overall numbers of birds are down, so far this month I've encountered 18 warbler species at Pheasant Branch Conservancy:

Northern Waterthrush
Golden-winged Warbler
Black-and-white Warbler
Tennessee Warbler
Nashville Warbler
Mourning Warbler
Common Yellowthroat
American Redstart
Cape May Warbler
Northern Parula
Magnolia Warbler
Bay-breasted Warbler
Blackburnian Warbler
Chestnut-sided Warbler
Black-throated Green Warbler
Canada Warbler
Wilson's Warbler

At present I think migration is running a little behind on account of the warmer weather we experienced last week. Weather plays an important role in migratory behavior. Nocturnal migrants favor a tailwind which allows them to virtually double their flight speed as well as preserve their fat stores. Some songbirds will migrate during unfavorable winds, but they'll do so at lower altitudes, thereby increasing the chance of colliding with man-made structures.

I use two meteorological websites to make birding predictions: Weather Underground's Wind direction/speed and Nexrad (Next-generation Radar). Many birders have heard how Nexrad can be used to view and track the movements of birds during the night. It serves as somewhat of an indicator of how "good" the birding may be the following day. However, lack of Nexrad activity during nighttime doesn't necessarily translate to slow birding in the morning. For example, inclement weather may have kept birds from migrating, so the woods might still be filled with migrants that travelled from previous days.

The above image shows highly suitable winds over the central US for bird migration the evening of September 4th. Later that night, about an hour after sunset, you can see how migration patterns after the wind direction and system fronts:

Professional ornithologists also use Nexrad to track migratory birds. Density estimations give ornithologists the ability to count the number of birds involved in migratory movements, specific direction routes, timing, speed, elevation, and correlation with weather patterns. Birds can detect storms by sight, smell, sound, humidity, and pressure. They'll attempt to fly around the storm cell, reverse direction, and possibly be forced to land. All of this can be detected and viewed live on Nexrad (check out the link to the primer below).

My favorite online Nexrad website is the National Center for Atmospheric Research/Research Applications Program - Real-time Weather Data or NCAR/RAP. To see live Nexrad maps, change the "Product" to "Regional Reflectivity" and leave the "Background" set to the default "black" option. For a quick snapshot, leave the "Loop Duration" set to "Single image." At this point you can either click on an individual radar station (three-letter codes across the states), or to see an entire map of US Nexrad data, select "Contiguous U.S." at the top.

Link: NCAR/RAP Nexrad

Link: Weather Underground Wind speed/direction

Link: Nexrad Ornithology Primer

Nashville Warbler © 2011 Mike McDowell


  1. Great post Mike (and gorgeous Nashville Warbler photo)! You know, I know this guy who runs a website...

    anyway, a little self promotion.

    I've got a faq with a video tutorial here on my website: http://www.woodcreeper.com/radar-migration-faq/

    Right now there are three active websites dedicated to posting daily interpretations of NEXRAD as it relates to bird migration, mine (woodcreeper.com), one in Florida (badbirdz2.wordpress.com) and a new one this year in Portland, OR (http://birdsoverportland.wordpress.com/)

    of course when I move to Madison in December I'll be starting a new one there ;) (unless someone else wants to!)

  2. Hey Mike- this got me thinking... what are the 'optimal' conditions during fall for conveying birds to Madison-area migrant traps? For Cape May NJ it's almost a no-brainer: Northwest winds associated with a passing cold front are the main driver of birds to the coast, after which point they work their way south to Cape May. A little less west in the wind, and the target migrant traps shift westward. A little east in the wind and you totally miss Cape May, favoring hotspots much farther inland. The assumption is that birds would 'rather' be moving along the Appalachians than down a dead-end coastal peninsula. As the shift westward happens, predicting good birding conditions becomes much less straightforward- since birds have more opportunities to disperse throughout the landscape (as opposed to 'stacking up' along the coast). Are the lakes around Madison significant enough to shape migrant stopover usage, or is it only at the greater landscape scale (with Lakes Superior and Michigan) that ecological boundaries to migration can be detected?

  3. Hi David,

    It's still somewhat of a guessing game for me. For example, though radar has shown pretty good movements of birds, timing the following day means everything. There were good birds before 9:00AM at Pheasant Branch yesterday, but low overall numbers. However, Sylvia Marek went there at 1:00PM and said the place was swarming with warblers. So, where were they in the morning? Where did they come from? Are these birds moving southward during the day as they forage from location to location? I suspect so.

    It seems to me the best fall birding in the Madison area is when there's favorable migration weather during the night, but a storm just to our south prevents them from moving on; rendering fall-out type conditions. Songbird migration along the big lakes, especially Milwaukee & Racine has a longer duration than what we experience inland.


  4. I love the Nashville Warbler photo, it really pops!