Weather and Songbird Migration: April 11, 2012
Dr. David Aborn, ornithologist
Dr. David Aborn

Dear Students:

Winter has returned—or at least normal early spring conditions! Either way, it has slammed the door on spring migration.

Those two cold fronts that moved across the country last week brought the first significant northerly winds of the season, and that is keeping birds bottled up along the Gulf Coast. Different areas seem to be seeing different species, but by far the best spot to see lots of migrants has been Texas. After the second front moved through over the weekend with the really cold air, people at the Gulf Coast Bird Observatory on High Island saw 23 species of warblers! They reported a "mammoth arrival" of Tennessee Warblers, as well as the largest arrival of Hooded Warblers seen in several years. They also saw lots of Indigo Buntings and the first Painted Bunting of the season. In Louisiana, Common Yellowthroats were the dominant species, while in Alabama it was Wood Thrushes. Birders in Louisiana also sighted the first Yellow-billed Cuckoo of the spring. North of the Gulf coast, things were pretty slow, as headwinds kept birds from making much progress. I heard a single Wood Thrush and a lone Common Yellowthroat over the weekend, and some others around the state reported the first Scarlet Tanagers and Eastern Kingbirds. Some White-eyed Vireos, Prothonotary Warblers, and yellowthroats were able to reach Oklahoma, and House Wrens have shown up in Nebraska.

Out West, birders have enjoyed a steady stream of migrants, as there have not been the northerly winds to keep birds grounded, especially in the Southwest. Three species of orioles were seen in Arizona (Scott's, Bullock's, and Hooded), along with more Bell's Vireos, Cassin's Vireos, Orange-crowned, Wilson's, Lucy's, and black-throated-gray Warblers. In California, the first Warbling Vireos and Olive-sided Flycatchers showed up, along with more Black-headed Grosbeaks and Nashville Warblers. Orange-crowned Warblers, Wilson's Warblers, and Cassin's Vireos made it as for as Oregon, but not much farther, as rain in the northwest made for poor flying conditions.

What Can We Expect This Week?
So, can the rest of us expect to enjoy the bounty of migrants seen along the Gulf Coast? Look to the weather map for some answers:

  • You see there are two high-pressure areas covering much of the country. This is what is bringing that arctic air so far south. Northerly winds will continue for a couple of more days, meaning things won't change much until the weekend.
  • By that time, the high pressure will have moved far enough east that the winds will shift to the south, allowing migrants to resume their journey north. That means people throughout the eastern half of the US should get out their binoculars and get ready for a nice influx of migrants!
  • There is another cold front moving through the Rockies right now, and it is bringing rain to much of the western US. That will prevent birds from making much progress for a few days. That front will bring some rain to the eastern US by early next week, and that will halt migration again, but in the west, conditions will improve and migration can resume.

How Do Migrants Survive the Cold?
You may be wondering how migrants might survive some of the cold temperatures we have been experiencing, especially in terms of finding food. Aside from having their own down coat to keep them warm, birds try to arrive with a supply of fat. In the US, we hear a lot about how Americans are too fat. Well, migrants want to be fat! Fat is energy, and it is how birds are able to fly such long distances. Having tailwinds means they do not have to work as hard to fly, and so they don't use up all their fat. Having some extra fat means that if it does turn cold where they are and insects are scarce, they have a built-in food supply they can use until conditions improve. If they do need to refuel, they do so at the places they stop at along their way, called stopover sites. These places are not only great places to see lots of migrants, but they are also critical to the survival of migratory species!

Take Care.

David Aborn
North Chickamauga Creek Conservancy
Chattanooga, TN