Migration Forecast: 4 – 10 May 2012

Benjamin Van Doren The Cornell Lab May 04, 2012

As several low pressure centers and their associated precipitation progress across the country, migration levels will vary more than usual. Primarily light to moderate movements will occur across more southerly portions of the West, whereas precipitation and generally unfavorable winds aloft will keep most migrants in more northerly portions grounded. Although a few areas of the Great Plains may see moderate to heavy movements early in the period and scattered movements for the remainder of the period, most areas will experience rather poor conditions for migration on most nights this week. Poor migration conditions will prevail more often than not across the Upper Midwest and Northeast, but birders should watch closely for marginally favorable migration conditions to develop, possibly producing moderate movements and fallouts may occur. The Gulf Coast and Southeast are in for another week of moderate to heavy movements, punctuated by a strong possibility of fallout conditions from Texas to the eastern Gulf late in the period.

See the week’s radar results here.

Male Bobolink, Minnesota, June. Photography by Mike Lentz.

Male Bobolink, Minnesota, June. Photography by Mike Lentz.


Bobolinks have recently arrived in some areas of the eastern US, and this week birders should see more widespread arrivals of this species in the East and Great Plains. Birders listening at night or during early morning may hear the distinctive “boink!” or “pink!” flight calls of passing Bobolinks, and those fortunate enough to have nesting Bobolinks close by will soon hear their amazing song, described by Arthur Bent as a “bubbling delirium of ecstatic music.” Bobolink is a species of special concern in some areas because of the loss of prairie, mixed grasslands, meadows, and agricultural areas producing hay. In addition, Bobolink is a long-distance migrant, with North American breeders moving primarily in the trans-Caribbean assemblage of migrants and wintering in the pampas of Brazil and Argentina. Members of the Lab’s eBird and Conservation Science teams are collaborating with The Nature Conservancy and New York Natural Heritage Program on a project funded by NYSERDA that brings together multiple datasets and analyzes bird migration data to help prioritize areas for wind energy projects that minimize biodiversity impacts. This project will also provide a forum for communicating this information to representatives of the wind industry. Bobolink is one of the focal species for this project, since its habitat requirements, migration strategies, and distribution make it an ideal study subject.Forecast

The forecast period will start off with continued south winds across much of the eastern U.S.  A series of low-pressure systems will track east across the Great Lakes and Northeast, and push a front southward. The front will eventually reach all the way to the deep South by the middle of the forecast period, with north winds dominating most areas east of the Rockies. This front likely will put the brakes on the first major influx of Neotropical migrants that has been occurring across the East this week. As migrants are stalled behind this weather, it may set up conditions for a major flight if favorable conditions should return in mid-May. High pressure off the Pacific Coast will keep winds mainly northerly along the West Coast for the entire forecast period with little precipitation expected.


As the period begins, migration in northern areas will shut down as scattered precipitation and northerly and westerly flow prevails, whereas southern areas should see extensive light to moderate movements in light and primarily southwesterly winds. By later in the weekend, and to begin the week, precipitation and continued unfavorable flow across most northern portions of the region will keep migration volume light at best.  The Desert Southwest and portions of the Great Basin and California will continue to experience reasonably favorable conditions and scattered light to moderate movements. This pattern will likely continue through the week for most of the region; in areas that are free of precipitation and that experience light and variable winds, scattered light movements will occur with locally moderate to heavy movements possible farther south and west. Birders in the Four Corners area and the extreme southeastern portions of the forecast region should watch the extent of precipitation forecast in the middle of the week; conditions may be favorable for local fallouts in migrant traps.As Pacific Coast migration winds down for many species, the Great Basin and Rocky Mountains should start to see their first significant waves of arriving Neotropical migrants. Species such as Western Tanager, Black-headed Grosbeak, Yellow Warbler, Wilson’s Warbler, and many others can be expected at desert migrant traps and at known breeding locations starting this week. The difference in arrival timing of these species along the Pacific slope and in the Intermountain West is striking, and something to watch for this week. For example, check out where Black-headed Grosbeak and Western Tanager have been reported so far this year, and watch the interior West start to fill in over the next two weeks. Along the Pacific Coast, northwest winds could produce good seawatching conditions from central California northward. Look for Sooty Shearwaters to arrive in numbers, and Red-necked Phalaropes should be on the move.

Great Plains

Southerly and southeasterly flow across much of the region will facilitate moderate to heavy migration to begin the period; birders should be aware, however, that forecast precipitation may create fallout conditions in some northern and eastern areas, warranting checks of migrant traps during the weekend. This will be especially true as a strong frontal boundary moves into northern portions of the region by Sunday night, creating the potential for such conditions in many central and eastern areas. The week begins with a strong low shutting down most movements across the region, with the exception of some locally moderate to heavy movements in the far south and east of the region. This pattern continues through much of the remainder of the period, as unfavorable winds are forecast to prevail in many areas; however, light winds, even if unfavorable, may allow moderate movements to occur, given the time of year and the potential pool of arriving birds to the south. Some areas of the region along the eastern Rockies may experience more regular light to moderate movements in light winds from midweek through the period’s end.

In many areas, this will begin the two-week peak of spring movement, with a high diversity of warblers, vireos, thrushes, and other migrants moving through. Flycatcher diversity should just begin to ramp up, although several of the later migrant species (e.g., Eastern Wood-Pewee, Willow, Alder, Yellow-bellied, and Olive-sided, will not peak until the second or third weeks of May). This is surely the most exciting time of the year for migrant landbirds in the Great Plains, and despite the forecast, migrant diversity should be peaking soon.

Upper Midwest and Northeast

The period begins with scattered precipitation and largely northerly and unfavorable winds aloft across the region; migrants will likely be grounded in many areas. Areas that do not see precipitation, however, will experience scattered moderate movements despite the largely unfavorable winds, given the time of the year and the available pool of birds trying to reach breeding areas. Much of the remainder of the forecast period will exhibit a similar pattern, with precipitation and unfavorable winds aloft expected to continue in most areas. Notable exceptions to the aforementioned pattern will include a moderate movement in western portions of the region to begin the week, including a potential for fallout conditions across the western Great Lakes and Upper Mississippi River valley, and moderate to locally heavy movements east of the Appalachians on Monday night and Tuesday morning. Birders in coastal portions of the region should watch the extent and intensity of rain from midweek through the remainder of the period, as the potential exists for migrating birds to interact with large areas of precipitation. If birds are migrating into these areas of precipitation, there is a strong potential for fallout conditions. Migrant traps should be checked from midweek through the remainder of the period, including inland water bodies, which will likely receive input from drop-ins of waterfowl, gulls, and terns.

As with the Great Plains, this week will mark the beginning of peak movement. The Upper Midwest has already seen some great days with high warbler diversity, and more such days are to be expected. By the end of next week, almost any species of warbler will be possible (including later migrants such as Blackpoll and even Mourning Warblers), although later migrant flycatchers like Willow, Alder, Yellow-bellied, and Olive-sided will not be expected to arrive in most areas until late in the following week. Early migrants like most waterfowl, Yellow-rumped Warbler, Chipping Sparrow, Palm Warbler, and Ruby-crowned Kinglets will become less and less common as the month progresses.

Gulf Coast and Southeast

Moderate to heavy movements continue in Texas to begin the period, decreasing in extent farther to the east where conditions are forecast to be less favorable. Western portions of the region will continue to see similar patterns into the middle of the week, whereas conditions in more eastern areas deteriorate with increasing prevalence of precipitation and unfavorable winds likely shutting down movements in many areas. Birders in the eastern Gulf of Mexico should watch for fallout potential, as light winds forecast in departure areas to the south combined with precipitation forecast near the coast. As the week progresses, precipitation becomes increasingly likely to shut down movements and to generate potential for fallout conditions (primarily inland). Of particular interest will be the arrival, late in the period, of a strong low pressure system; the forecast timing and extent of this system suggests a potential for fallout conditions to develop in coastal areas from Texas to Mississippi; furthermore, this system may continue to produce fallout conditions farther east as it moves toward the Atlantic. Note, the forecast period ends in western portions with most migration shut down after frontal passage, and with rain and in eastern portions with moderate to heavy movements in areas free of precipitation ahead of frontal passage.

With most nesting species already on territory, most of the migratory arrivals will have already happened. Shorebirds and terns (e.g., Black Tern) will continue to pass through in numbers. Northern nesting warblers, thrushes, flycatchers, vireos, and other species such as Scarlet Tanager, Rose-breasted Grosbeak, and Indigo Bunting, will continue to stream through the region. Check coastal migrant traps, ridges and mountaintops, and other concentration points to find maximum diversity of landbirds, and as always, watch the weather!

Posted 4 May 2012 by Marshall Iliff, Andrew Farnsworth, Brian Sullivan, and Christopher Wood of the Cornell Lab of Ornithology and David Nicosia of NOAA, on behalf of Team eBird and BirdCast.