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Posted by Alex Harper on 22:28:46 03/28/11
Migration is the hot topic on the board right now. I think that instead of just heading out to our local migrant traps and hoping for the best, we should understand what is driving what is the most complex of avian ecology.
Radar activity is fun to watch, but unless we understand the weather, we can't make any solid predictions as to where they are going to land. That said, start at where the birds are right now. Any migrants headed to South Florida are bulking up and staging in the Yucatan, Mexico, Cuba, Jamaica, and possibly as far east as Hispaniola. The past (one to several days) and current (today and tonight) conditions at these locations play the role in the degree of movement.
A site that I find most useful is wunderground.com. Under "enter a location", type Cancun, Mexico for example (or Merida, Mexico, Havana, Cuba, etc). Scroll down to the "WunderMap" and click on it. A NEXRAD Radar layer is provided by default, but scroll down under the map controls and check "Weather Stations". Conditions at the weather stations in Cancun, MX should appear. On the right side of the page is a legend explaining how to interpret wind direction, and clicking on the individual stations provides information on current conditions at the station.
Now zoom out so that you can see the Yucatan, Cuba, and Florida in the same frame. You can see, more or less, what the conditions throughout the region are like. Intuitively we know to look at changes in wind direction and weather events over Florida to predict a fallout to any degree. Using this map though, you can see if birds may even be moving from their staging ground.
Here is another useful resource: http://weather.org/weatherorg_records_and_averages.htm
This site allows us to access past weather at a given location. For example, type "Miami, Florida" under the location, and plug in the date April 14, 2009. It will navigate you to wunderground.com/history. The information from that day is pulled up, reading that there was little precipitation and wind conditions were 11 mph out of the south. At the top of this page, click on "Next Day". On April 15, 2009, winds have shifted to 7 mph out of the west southwest, with some strong gusts. Now click "Next Day", navigating to April 16, 2009. Wind is out of the north at only 7 mph, with gusts up to 20 mph. Click "Weekly" to see a chart displaying the wind history the week of April 12-18, 2009. Now compare April 14, 15, and 16 to TAS reports. On April 15, Toe wrote a post titled "A.D. Barnes Slow, 4/15". April 16 was a different story, with 15 warbler species being at A.D. Barnes.
The difficulty is locating where a front or two different wind systems meet or occlude, or deciding if conditions for birds to leave the Caribbean are favorable. Birds landing along the Gulf barrier islands or South Florida in the spring are almost always those low or depleted of fat reserves, and those with enough fat and favorable winds can easily pass by our migrant traps. Birds in Cuba waiting several days for south winds will accumulate enough fat to easily jet past Florida throughout the night and into the next day once they decide to take off, whereas a bird spending one day in Cuba after arrival may only have enough fuel to hop over to Miami the day following.
Anyway, there are my two cents. I had the privilege to take a meteorology course with the University of West Florida's Dr. Jason Ortegren last year, and aside from brilliantly teaching me about weather and climatic processes, he got me interested in his field. Since applying what I have been taught, I am becoming more accurate in predicting the movement of Trans-Gulf migrants during the spring. With wunderground.com, of course. Hopefully these sites provide useful to you all as well.
Alex
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