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April 21, 2010
Dr. David Aborn

Dear Students:

Well, it has finally happened...a MAJOR fallout! Over the weekend a low pressure area developed around west Texas. This was mainly a rain event, so once it passed there really weren't any strong winds to keep birds grounded for very long. Thus, the rain forced birds to land and then they could take off again in large numbers. Because we are around the peak of spring migration along the Gulf Coast, the numbers of birds being seen the last couple of days has been staggering. One researcher at the Gulf Coast Bird Observatory on High Island, TX said it was the largest movement of birds in recent memory.

Before that storm system developed, winds had been southerly, and skies had been clear, which allowed many of last week's migrants to make a lot of progress north. In a previous report I mentioned Frozen Head State Park in northeast Tennessee. Well, it proved to be a good spot this week, with 46 Blue-headed Vireos, 81 Black-throated-green Warblers, and 29 Ovenbirds seen. Birders in Washington, DC had their first Northern Parulas, Black-throated-green Warblers, Yellow-throated Warblers, Black-and-white Warblers, Worm-eating Warblers, and Ovenbirds. Some places very far north are starting to see the first migrants trickle in, with an early Rose-breasted Grosbeak in New Hampshire, the first Chimney Swifts arriving in Wisconsin, and House Wren showing up in Michigan and Minnesota.

While that storm system developed too far to the east to give the western US a fallout, a lot of birds were still on the move. Birders in California reported large numbers of Yellow Warblers, Lazuli Buntings, and both Blue and Black-headed Grosbeaks. The south winds also helped push migrants into the Northwest, with Washington seeing swallows, Common Yellowthroats, Wilson's Warblers, Orange-crowned Warblers, Yellow-rumped Warblers, and a lone Black-throated-gray Warbler.

What Does This Week’s Weather Mean for Migration?
The coming week could be another good one:

  • A strong cold front is starting to move across the country. That, combined with the fact that migration is peaking in the southern US means there could be some more good fallouts along the Gulf Coast by the end of the week, and in the eastern US by the weekend.
  • Folks out west could be seeing birds landing today, as there is rain over much of the West Coast right now.
  • Once the system clears out and winds shift to the south a couple of days later, people in the northerly parts of the US should start looking for new arrivals.

Fallouts are very impressive to see, so get out there and be a part of it!

How Do Researchers Know How Many Birds Are Around?
We have several ways we can see how many birds are around. Aside from just going out with binoculars and looking and counting, we can capture birds in special nets, and we can also use our ears and radar.

Mist Nets: Captures
I and many other researchers who study migration use special nets called mist nets. These are soft fabric nets that are hard for the birds to see. The birds fly into them unhurt, and then researchers gently take them out, put US Fish and Wildlife Service identification bands on their legs, examine their health, and let them go. The person I studied under has a study site at Johnson's Bayou in southwestern Louisiana. He reported to me that April 20 they captured over 500 birds!!!! That is an incredible number! During my Ph.D research, we had some days where we caught between 200 and 300 birds, and that was just insanely busy. They must have been totally up to their eyeballs in migrants!

Radar: “Seeing” Migration at Night
Many songbirds migrate at night because 1) the air is less turbulent, 2) there aren't as many predators around, and 3) they can use the stars to help them find there way. Many migrants fly in flocks and they call to help keep in contact with the flock. On a night with a lot of migration going on, you can actually hear their calls. Someone listening to these calls in Houston, TX Monday night reported hearing between 60 and 180 calls per minute!!! The majority of those calls were from thrushes, Indigo Buntings, and tanagers. Flocks of migrants can also be picked up on National Weather Service radar; the same ones you see on your local news every day. Here is a loop from radar stations across Texas from last night (April 20) to show birds taking off shortly after sunset. All that green and yellow you see is not rain; those are birds resuming their migration!

Take Care,

David Aborn
North Chickamauga Creek Conservancy
Chattanooga, TN