Migration arrivals continued across portion of the West, while the floodgates began to open in many areas of the East. The 5-12 April 2013 animation shows the week’s movements relative to synoptic weather conditions.
Light to moderate movements began the period and continued into the early week in the Desert Southwest, Four Corners, and California, as scattered precipitation kept many migrants grounded to the north. Aside from light movements in California on Monday night, most movements halted in high pressure over the Pacific Northwest and passing disturbances over the Four Corners. However, conditions improved across much of the region as the week continued, and increasingly widespread light to moderate movements spread across the region by Thursday. Birds on the move this week included Marbled Godwit among other shorebirds, Vaux’s Swift, continued large movements of swallows, Yellow-breasted Chat, Black-headed Grosbeak, and Savannah, Fox and White-crowned Sparrows.
High pressure kept migration local and light across the region to begin the forecast period, and passing storms generally disrupted any continuous nights of movements across the region for the forecast period. However, hints of what is to come, though short lived, appeared over the weekend and to begin the week, as local light to moderate movements occurred as a warm front advanced toward the Mississippi. These movements were generally halted by the rapidly changing and mostly marginal at best conditions during the period. High pressure built in to end the period, with little activity on radar apparent. Birds on the move this week included Green-winged Teal, Swainson’s Hawk, Solitary and Upland Sandpipers, Franklin’s Gull, Ruby-throated Hummingbird, White-eyed Vireo, Hermit Thrush, House Wren, Brown Thrasher, and Chipping Sparrow.
Upper Midwest and Northeast
Scattered light movements kicked off the period as a cold front advanced toward the region. As high pressure moved out into the Atlantic, the flood gates opened. Saturday night saw light to moderate movement across much of the region, including some locally heavy movements in the central Mississippi River valley. The forecast for southern overshoots from last weekend did not bear fruit in New England, discussed in a previous post this week. Light to moderate movements persisted in a number of areas, depending on local conditions associated with a complex frontal boundary of cold and warm fronts bisecting the region. This complex frontal boundary spawned numerous waterbird fallouts, including Long-tailed Duck, Bonaparte’s Gull, and Caspian Tern. It was not until Wednesday and Thursday that the storm systems organized and simplified into a strong passing front that generally halt most (but not all!) migration across the region.
Our collaborator Dave Nicosia at NWS-Binghamton forwarded an image from local midnight on 10 April 2013 at Binghamton.
Birds on the move this week included Broad-winged Hawk, Bonaparte’s Gull, Caspian Tern, Northern Flicker, Hermit Thrush, Ruby-crowned and Golden-crowned Kinglets, Blue-gray Gnatcatcher, Louisiana Waterthrush and Palm Warbler, and Swamp, Field, and Chipping Sparrows.
Gulf Coast and Southeast
High pressure built over the Mississippi River delta, bringing a return of light to moderate movements to Texas in improving southerly flow to begin the weekend. The favorable conditions expanded over much of the region over the following days, facilitating widespread light to moderate movements and even some locally heavy movements in Florida and Georgia. This pattern came to a halt as a new cold front crossed into the region on Thursday, shutting down migration to the west in northerly and westerly flow and facilitating continued movements to the east in southerly flow.
A common pattern observed on radar during April and May is trans-Gulf migration from the Caribbean departing from Cuba and arriving in the keys or on the mainland. Scattered showers, the blocky patterns drifting north over the Florida Straits, were not the only targets over the water last night! Migration exodus from Cuba appeared over the Straits as a moderate to heavy movement of inbound birds (and insects and bats). Note that as birds reached the Key West radar, green pixels dominate the image. Because the radar beam rises as it moves away from the radar, in this case at a 0.5 degree angle of elevation, the radar scans lower altitudes closer to the station; and this pattern of increasing colors suggests that higher densities of birds were moving at lower altitudes. The Key West radar detected the upper bounds of migrant departures from Cuba first, and then gradually detected more and more of the volume of the movement as birds approached the radar.
Birds on the move this week included Broad-winged Hawk, Chimney Swift, Great Crested Flycatcher, Eastern Wood-Pewee and Western Kingbird, Yellow-throated Vireo, and Worm-eating, Hooded, Prothonotary, and Black-throated Green Warblers.