Migration Report: 31 March – 5 April 2012

Benjamin Van Doren The Cornell Lab Apr 06, 2012

Last week’s BirdCast forecast made a couple predictions about fallouts that we focus on this week. These include a widespread waterfowl fallout in the Northeast, which we discuss in some depth to help eBirders prepare for similar events in the future. Along the same lines, last week’s mention of possible passerine fallouts on the Gulf Coast also came true, at least very locally. This too is a good phenomenon to understand, and an incredible one to witness, and is discussed in some extra detail. Detailed analyses of the patterns seen from weather and radar are also included, as always. We also encourage you to review the previous week’s forecast and to use eBird’s View and Explore Data tools to see if some of the other migration predictions came true. We hope you enjoy this BirdCast migration report–a special edition dealing with “fallout.”

See the week’s radar results here.

Long-tailed Ducks had impressive fallouts in the Northeast.

Long-tailed Ducks had impressive fallouts in the Northeast.

About Fallouts

At a basic level, a fallout is any event that causes migrating birds to be grounded. In almost all cases, fallouts involve two main elements: 1) a large number of birds must be aloft and on the move; 2) inclement weather–usually precipitation but occasionally just fog or unfavorable wind–then blocks that movement and causes them to land. So as a birder, you want to watch for good migration conditions (clear and southerly winds in spring, northerly or northwesterly in fall) which then intersect lines of precipitation or a large region of unsettled weather. Squall lines with solid bands of heavy rain are sure to “knock down” all birds they encounter, while patchier areas of rain may allow some birds to fly through or around the rain until they finally encounter rain that they cannot fly through. The strength and magnitude of a fallout thus varies not only by how many birds are on the move, but also by how strong the blocking event is and whether some birds can fly through it or around it.

These basic building blocks of a fallout are the same for songbirds as they are for waterfowl or shorebirds, although the types of places you might look for these groups will obviously differ. Even hawks can have “fallouts” at times, such as when thousands of Broad-winged Hawks are forced to the ground. The most impressive fallouts (and also the most costly for bird populations) tend to be when fallouts occur over water, forcing weakened birds to struggle to shore, concentrating on islands or coastal “migrant traps” regardless of habitat considerations. Although these conditions are enjoyable for the birder, it is important to understand and remember the large number of birds that probably do not survive under these circumstances.

When you think you might be experiencing a fallout, you should continue birding to try to make the most of it–fallouts are rare events. As you continue your birding, if you see evidence of birds continuing to arrive, or changeover in the species composition before your eyes, you might just find a good spot and stay there. On the other hand, if it seems like the fallout happened overnight, it might be most interesting (especially with waterfowl) to check multiple spots nearby to see how the composition might differ and how widespread the phenomenon is. For waterbirds you will obviously want to check bodies of water (even very small ones can be good in big fallout events). For shorebirds, you will want to check any body of water with a beach, but be sure also to check wet fields, where shorebirds often land (even athletic fields or puddles in parking lots will suffice at times). For passerines, “islands”, including true islands as well as isolated patches of habitat, are usually the best places to check. Peninsulas and coastlines are the second best concentrating mechanisms, especially when fallouts happen over open water. High points too, like mountains or hilltops with good habitat, can sometimes be a real magnet for passerines, as these often stand up tall above the surrounding landscape and can often provide islands of habitat that are attractive to passerines. Sites like Garret Mountain, NJ, and Mount Auburn Cemetery, MA, are well-known sites for spring warblers that combine high ground and isolated “islands” of habitat. In open grasslands and deserts small groves of trees and even towns can make incredible concentration points for landbirds. Said differently, concentrations are most likely to occur in isolated patches of the most appropriate habitat for each species.

Waterbird fallout in the Northeast

Last week’s BirdCast forecast included this blurb:

“Stormy conditions early in the week appear poised to force down  Long-tailed DuckHorned Grebe, and perhaps even a few  White-winged Scoters moving between the Atlantic Ocean and Great Lakes. These species can even show up on ponds during inclement weather, so get out and check ponds, lakes, and other water bodies for these waterbirds. The extent of overland migration for Long-tailed Duck, in particular, is under-appreciated by most birders. Note the pattern of observations between major wintering areas from the Chesapeake to New England, and staging areas in the Great Lakes (where they also winter). Seriously. This is very cool. Click this    link. And compare with January and February of this year. You can also listen for migrating Long-tailed Ducks calling as they fly overhead at night.”

Starting on Saturday 31 March, and particularly on Sunday 1 April, there was a widespread waterfowl fallout across much of Pennsylvania and western New York. The week’s radar image for 31 March is particularly illuminating, and represents the period just past midnight on 31 March. Conditions in coastal New Jersey and Chesapeake Bay are suitable for migration and the blue shade represents birds aloft. Just to the north, slating across southern Pennsylvania and northern New Jersey, is a strong frontal boundary with heavy rain (the yellow areas). When migrating waterfowl encounter weather like this, they must land wherever they can…a fallout.

Fig. 1. Long-tailed Duck map for 31 March-6 April 2012. Most of the inland records in Pennsylvania, New York, and nearby states were a result of the 31 March-1 April fallout.

Fig. 1. Long-tailed Duck map for 31 March-6 April 2012. Most of the inland records in Pennsylvania, New York, and nearby states were a result of the 31 March-1 April fallout.

Fig. 2. Long-tailed Duck map for 1-6 April 2012. This view is interesting not only to see how many inland birds were seen in this period (many of them from 1 April only), but also to highlight regions where Long-tailed Ducks seem to have disappeared. Chesapeake Bay, New Jersey, and the tip of Long Island have far fewer Long-tailed Duck points now.

Fig. 2. Long-tailed Duck map for 1-6 April 2012. This view is interesting not only to see how many inland birds were seen in this period (many of them from 1 April only), but also to highlight regions where Long-tailed Ducks seem to have disappeared. Chesapeake Bay, New Jersey, and the tip of Long Island have far fewer Long-tailed Duck points now.

The eBird community was definitely aware and many birders made a conscious effort to seek out grounded waterfowl.

For example, Drew Weber checked spots in Pennsylvania. Check out his lists from multiple viewpoints at Bald Eagle State Park, including 16 species of waterfowl (and 199 Long-tailed Ducks, 99 more Long-taileds nearby, another list with 50 Long-tailed Ducks, and this list with 14 species and 362 Long-taileds. His lists are exemplary with very careful counts and very good details.

For those of us on Team eBird, this fallout was well-timed (weekend!) and well situated for us to enjoy it in the upstate New York area. eBird Project Leader Chris Wood got out to a number of water bodies in Tompkins and Cortland County, New York. His more interesting observations included 3 Red-necked Grebes at Dwyer Memorial Park, 4 White-winged Scoters at two unusual locations, and Long-tailed Ducks and Horned Grebes in a number of places. Somewhat surprisingly, presumed migrant adult Lesser Black-backed Gulls were also grounded by the weather in two places, including two in a large grassy field with other gulls. Of particular interest was that Chris checked one place (Dryden Lake) in the morning and afternoon, and the disparity between the species totals demonstrates that some of the ducks and possibly even grebes (!?) were departing during the day to continue their migration once conditions allowed.

Since this week was one of our quarterly eBird meetings in Ithaca, and since Marshall Iliff was driving across New York, Chris gave him a heads up on Sunday to check one particularly productive reservoir along the route. The results? Seven waterfowl including Long-tailed Duck and both Horned and Red-necked Grebes.

Even our boss got into the action. When not riding herd on the other members of Team eBird, Steve Kelling can be found birding his regular routes around his home in Caroline, NY. But one of his other passions is nocturnal flight call recording: this week his recordings captured Long-tailed Ducks on 4 April (recordings embedded in his list), 5 April, and 6 April. Northeastern observers should continue to listen to the distinctive calls of Long-tailed Duck this week, which might be heard on clear and quiet nights.

Landbird fallout on the Gulf Coast

Fallouts, both of waterbirds and landbirds, can be highly localized.

Last week’s BirdCast forecast included this:

“With the threat of precipitation increasing through Tuesday night, and a potential for wind shift during the day on Tuesday [3 April], birders should be aware of the potential for coastal fallout of circum-Gulf and trans-Gulf migrants. Conditions for fallouts are forecast to continue to move eastward along the Gulf Coast, providing birders opportunities for trans-Gulf groundings in MS, AL, and the panhandle of Florida.”

Returning to the radar imagery, focus on Louisiana on 3 April. In the evening, squall lines proceeded offshore and an isolated area of precipitation can be seen covering much of southern Louisiana. Given that conditions were otherwise good for bird migration, there were probably widespread arrivals of migrants throughout the Gulf Coast. But those birds on a track to arrive over southern Louisiana would have encountered northerly winds and rain, forcing them down from high migratory heights. When this occurs, many birds migrating over water drop low to the surface of the water and fly just above wave height, in an attempt to minimize the headwind. This is one of the most perilous situations for a bird, and when they encounter a place to perch and ride out the storm, they will immediately stop. If that place provides cover, so much the better. Grand Isle, Louisiana, is a perfect stopping point, as it is an elevated town that rises from the Louisiana marshes and has patches of forest that are literally the only trees and dry ground for miles. It is a well known migrant trap (like High Island, Texas) and Louisiana birders make regular pilgrimages there to look for migrants.

At least two eBirders went there on 4 April, and demonstrated that a significant (but localized) fallout indeed occurred at Grand Isle. Although some of the species counts are mundane, the Prothonotary Warbler count alone show what a significant event this was. Keep in mind that Grand Isle is only a few miles long, and then try to envision seeing 205 Prothonotary Warblers crowded into 3 or 4 small woodlots!

Robert Purrington’s list (201 Prothonotaries)

Dan O’Malley’s list (115 Prothonotaries)

Weekly Summary

Below are our weekly summaries of weather and migration activity, from our BirdCast radar analysis. See the radar animation here to follow along with the week’s movements and migration.

West – The Pacific Northwest and northern Rockies began the week with precipitation. Portions of California and the desert Southwest experienced more widespread light migration than visible on radar in past weeks, including widely scattered areas of moderate movements in California.  These movements are presumably birds, although one cannot rule out insects and other aerial plankton from this imagery. The cold front that moved across much of the West by early Sunday morning brought precipitation to much of the western and northern portions of the region but allowed scattered light migration amounts to occur across portions of the desert Southwest north into Colorado. By early Monday, most migration had shut down with the exception of areas farthest west of the frontal boundary, such as close to the immediate coast, where light migration was apparent; by early Tuesday, coastal movements had expanded north into the Pacific Northwest, where light to moderate movements occurred in advance of an approaching storm system. As this system came ashore and then gradually moved east across the norther portions of the region, migration shut down through the end of the week. However, southern California and the Desert Southwest continued to experience light migration during this time, gradually diminishing as the front pushed eastward.

Great Plains – Moderate to heavy migration occurred over the weekend across the southern and eastern Plains states, as far north as the Canadian border. This pattern continued into the early portion of the week, albeit in primarily light to moderate movements. As this system moved into and through the region, unfavorable wind conditions and some intense precipitation shut down most nocturnal movements, with the exception of areas to the south and east of the frontal boundary. By mid week, with low pressure slowly proceeding east out of the region, light migration was widely scattered far to the north and west of the low. Migration volumes increased to light and moderate as high pressure followed into the region, with light winds and ameliorating temperatures continued to push into the northern Plains states. By week’s end, widely scattered light migration occurred primarily from the central portion of the region north to the border with high pressure ensconced across much of the center of the nation.

Upper Midwest and Northeast – With the exception of the waterfowl fallout discussed above, most of the region was quiet from the migration perspective. Prevailing high pressure across much of the Great Lakes late in the weekend allowed light migration to take place across portions of the Midwest, even reaching moderate levels in some areas, as calmer than forecast winds and a stalled front to the south did not stop birds from taking flight. This pattern continued into the very early portion of the week, when the western Great Lakes experienced some moderate movements, generally diminishing in amount farther south and east toward the frontal boundary. With low pressure parked just west of the region by Tuesday early morning, light to moderate migration occurred over many areas of the upper widest including some heavy movements in the far north and west of the region. By midweek, with northerly flow again apparent in many areas, scattered light migration occurred, building to more moderate levels in the far north and west of the region by Thursday morning; this pattern continued through Friday. The Northeast saw no significant movements apparent on radar, with the notable exception of Tuesday night and early Wednesday morning when light movements were apparent along the coast of New Jersey and southern New York in light winds.

Gulf Coast and Southeast    – Scattered heavy movements among more widely apparent moderate movements were the norm in Texas at the beginning of the forecast period. The remainder of the region experienced varying degrees of movements. The Florida Keys saw light to moderate migration amounts from inbound Cuban and Caribbean migrants. Early in the weekend, scattered precipitation in the Southeast, some of it intense, kept migration amounts to light in many areas, but where precipitation did not fall, migration reached moderate levels. However, by later in the weekend, with the effects of high pressure to the west and south, migration amounts gradually diminished in most areas of the Southeast to widely scattered light movements. Early week saw widespread light to moderate movements across much of the region, particularly away from coastal areas. From Tuesday through Thursday morning, scattered but intense precipitation occurred in several areas of the region, interacting with nocturnal and diurnal migration and (likely) causing fallouts in the some areas of interaction from Louisiana east through Florida during this period. Note, beginning midweek, the Florida Keys got several inputs of Caribbean migrants from Cuba and points south, including an arrival interacting with precipitation early Thursday morning. In precipitation free areas, light to moderate movements were apparent in many areas around the region; Texas was a notable exception, with generally heavier movements, especially farther south and toward the coast. By the week’s end, as the frontal boundary continued to push south and east, only southernmost Texas experienced moderate to heavy migration, getting lighted around and just passed the dry, frontal boundary.

Posted 6 April 2012 by Marshall Iliff, Andrew Farnsworth, Christopher Wood, 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.