Weather and Songbird Migration: March 21, 2012
Dr. David Aborn, ornithologist
Dr. David Aborn

Dear Students:

It has been feeling more like summer than spring in many places, but the birds' minds are still on spring migration!

In last week's report, I mentioned that the southerly winds that are giving so many people nice warm temperatures would help migrants make some progress northward, and that is what has happened. Louisiana Waterthrushes have shown up in Oklahoma, Illinois, and Pennsylvania, and Tree Swallows have made it as far as Missouri and Massachusetts. While numbers have not been high, there has been a good variety o species arriving from the tropics.

Explaining the Rain
If you look at this week's weather map, you'll see a feature I have not talked about before. Notice that the front over the middle of the country is both red and blue; that means the front is stationary (not moving). Last week I mentioned that front and how it would move across the country. Well, the high pressure area off the eastern US is a strong one, and has not allowed that front to move. As a result, the southerly winds have allowed moisture from the Gulf of Mexico to interact with the front, producing heavy rain. That rain has been forcing migrants to land in Texas and Louisiana.

Last Week's New Species
As I just mentioned, numbers of migrants have not been high enough to produce a major fallout, but quite a few new species have shown up. People in Louisiana reported the first Prothonotary Warblers, Common Yellowthroats, Hooded Warblers, Worm-eating Warblers, Red-eyed Vireos and Great-crested Flycatchers of the spring, while Texas reported Indigo Buntings, Orchard Orioles, Eastern Kingbirds and Scissor-tailed Flycatchers.

Clear skies and southerly winds have also helped migrants out west. In Arizona, Bell's Vireos, Scott's Orioles, Lucy's Warblers, and Wilson's Warblers have arrived, and Warbling Vireos, Bullock's Orioles, Tree Swallows, Wilson's Warblers, and Western Kingbirds are showing up in California, and some of those birds have made it as far as central California.

What Can We Expect This Week?
So, can Texas and Louisiana expect more migrants to grace their shores, or will the rest of us be able to join in the fun?!

  • The high pressure area I mentioned is starting to break down, which will allow that front to finally move east over the weekend. It is not an especially strong front, meaning the north winds behind it are not strong, so it shouldn't slow migrants down too much.
  • While migrants may be halted for a day or two in the east, winds in the center of the country will be shifting to the south, allowing many of those birds in TX, and LA to move into the Midwest.
  • The western US continues to have good flying weather, so new migrants should continue to arrive and some of the birds I mentioned will have no problems continuing their migration.
  • Another cold front is moving into the Pacific northwest, but it is too early to say how it might impact migration. It will have to wait for next week's report!

Take Care.

David Aborn
North Chickamauga Creek Conservancy
Chattanooga, TN