Migration Report: 20 – 26 April 2012

Benjamin Van Doren The Cornell Lab Apr 27, 2012

This was an exciting week in spring migration as things really began to ramp up on a continental scale. The West saw significant movement throughout the region with a consistent flow of birds from the south, and some of the heaviest migration to date for the Pacific Northwest. After a slow start during the weekend, things really ramped up over the Great Plains and we saw some very high densities of birds trucking through the middle of the country by early in the week. The Upper Midwest has yet to realize the wave of migrants yet to come, but did see some variable migration result in a handful of new spring arrivals this week. The Northeast too is waiting for the big push, but did have several good movements into the Ohio Valley and Mid Atlantic by the end of the week. The Gulf Coast and Southeast were hotspots of activity throughout most of the forecast period, and with birds streaming in from Mexico and the Caribbean we only expect it to get better.

Have a look at our predictions from last week.

An advancing cold front last Saturday spurred widespread migration along the Atlantic and Gulf Coasts.

An advancing cold front last Saturday spurred widespread migration along the Atlantic and Gulf Coasts.

Southern Vagrants and Early Overshoots
As the latest frontal boundary moved to the East Coast between Sunday and Monday, strong storms formed over New England. Heavy precipitation coupled with strong circulation around the storms triggered some migration over coastal New England at least as far north as the precipitation and unstable atmospheric conditions extended. Given the general southerly flow along the extent of the coast, and the unfavorable conditions caused by these storms, birders in Maine were keen to check their local haunts once the conditions cleared. Those who sought out birds in coastal migrant traps were not disappointed, as demonstrated in this report by Maine birder and rarity sleuth Derek Lovitch:

“The track and strength of the recent storm suggested the possibility for southern vagrants and early overshoots.  Jeannette and I headed to Biddeford Pool this morning hoping to test this hypothesis, and we were rewarded with:

– 1 female BLUE GROSBEAK, East Point.
– 1 male HOODED WARBLER, corner of 1st and 3rd Streets.
– 1 immature male SUMMER TANAGER, 1st Street about 100 ft east of 3rd.

Regularly occurring migrants were limited to 1 Palm Warbler and an ample number of White-throated and Chipping Sparrows.”

This was a great week for migration in the West, and our forecast for California, the Great Basin, and the Desert Southwest was pretty spot-on. We predicted only light migration over the Pacific Northwest because of the threat of precipitation, but while precipitation did indeed precluded migration at the end of last week, by the weekend the region saw the heaviest movement yet this spring as birds pushed north into Oregon and Washington. Heavy precipitation failed to materialize in the Northern Rockies, and as a result migration proceeded nicely throughout the early part of the week. After the weekend things tapered off a bit in the north but birds continued to move in good numbers to the south and west. By the end of this week we saw heavy precipitation shutting things down along coastal California, Oregon, and Washington, while the Desert Southwest continues to experience moderate to heavy flights.

Great Plains
Our predictions for the Great Plains region were generally good overall. The low pressure systems which did affect the area were primarily dry, which did reduce the amount of precipitation as well as the chance of fallout conditions, but otherwise our expectations of migration activity were borne out in the nightly radar. Opposing winds and precipitation precluded any major migration early in the forecast period although some localized migration was apparent over Kansas and Nebraska at the beginning of the weekend. Things picked up considerably, though, at the beginning of the week when a frontal boundary set up along the Rockies and brought southerly flow to the region. This triggered widespread migration along the entire central region from Texas to the Dakotas and resulted in many first spring arrivals. By midweek birds were still moving through, although migration intensity was reduced by the presence of two fronts running east to west across the region. Heaviest migration continues to be in the southern Plains with lighter movement to the north.

Upper Midwest and Northeast
As predicted, the forecast period started out slow for the Upper Midwest with heavy precipitation associated with low pressure over Iowa and Michigan, while the Northeast experienced heavy migration under optimal conditions prior to the weekend. While not extensive, localized movements across the Upper Midwest did result in some new birds being shunted up into eastern Wisconsin and against Lake Michigan. The vast majority of FOS Black-throated Green Warblers occurred in the area predicted by these winds and weather conditions (see map in eBird). Conditions deteriorated over both regions by the end of the weekend as heavy precipitation and unstable conditions became the norm. By the end of the weekend variable conditions over the Upper Midwest produced mixed results in terms of migration with a few birds making their way into Iowa, Illinois, and Michigan. By the beginning of the week the region saw its first reports of Yellow Warblers, as well as multiple Warbling Vireos, and as of today, Baltimore Orioles. With the front pushed against the East Coast and northwest winds building in behind it, poor migration weather dominated the first half of the week in the Northeast, with some small exceptions along coastal New England. Things began to improve by Tuesday night, though, as southerly flow and migration returned to the Mid Atlantic and Ohio Valley. This eventually led to heavy and widespread migration Wednesday night as far as southern New York. Wood Thrush, Blue-headed Vireo, and a smattering of warblers are making their way into the Northeast now, and the future is looking good for diversity over the next week.

Gulf Coast and Southeast
As a strong cold front swept eastward across the US, moderate to heavy migration moved north ahead of it. The precipitation we anticipated for early in the forecast period over Texas failed to materialize during the hours of migration, and hence migration activity was hot and heavy from Texas to the Carolinas in the latter half of last week. Fallout conditions did occur as anticipated over the weekend, as storms and migrants mixed over Florida and along the Southeast Coast.

On Saturday night, a strong surface low spinning over northwest Florida brought heavy rain and strong southwesterly winds to most of the peninsula. Birders weren’t running for cover though, as they anticipated some of the best birding of the spring the following morning. A moderate number of birds left Cuba that night heading for Florida, but even more birds were migrating beyond the radar’s view: from the Yucatan Peninsula. Trans-Gulf migrants began pouring into West Florida on Sunday morning and eventually resulted in one of the best birding days in recent memory. From Key West to the Big Bend region of the Panhandle birders were treated to a great diversity and density of warblers, thrushes, tanagers, and grosbeaks. The epicenter appeared to be the well-known migrant trap Fort Desoto, in Pinellas County, where over four days birders tallied 27 species of warblers including several Ceruleans, and 4 species of thrushes. To really appreciate the density and diversity, check out this ebird checklist from the fallout:
Fort De Soto Park – 24 April – Graham Williams

At about the same time as the big Florida event, a second front was pushing into west Texas triggering the beginning of another wave of migrants that continues to the time of this writing. By Monday, most of the area east of Texas was under northerly winds and migration was minimal at best. On Tuesday, however, the Texas coast came uncorked, and both Circum-Gulf and Trans-Gulf migrants began to stream into the region. Wednesday night saw a great influx of new birds across the Southeast, with heavy migration continuing up through Texas, Arkansas, Louisiana, Alabama, and Florida and many birds moving through the Appalachians into the northern reaches of the region. Migration across the Florida Straits was also high on Wednesday night as birds made landfall throughout the Florida Keys and southern Florida Thursday morning. As of this writing heavy Trans-gulf migrants are making landfall along the TX, LA, AL, and FL coasts.

Posted 27 April 2012 by David La Puma of the University of Delaware, and Andrew Farnsworth and Brian Sullivan of the Cornell Lab of Ornithology on behalf of Team eBird and BirdCast. Special thanks to David Nicosia, our partner at NOAA, for the weather maps and analysis in our BirdCast predictions.