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