Migration Forecast: 27 Apr – 3 May 2012

Benjamin Van Doren The Cornell Lab Apr 27, 2012

While most of Team eBird is down in Texas making Big Day history, I,David La Puma, have been charged with filling in for them in writing this week’s migration forecast. In doing so, I have also called upon a team of migration experts from across the country to weigh in on the regional components of this most exciting BirdCast. Thanks to Drew WeberGreg HaworthMax HenschellTom Auer,Tim SchreckengostAngel and Mariel Abreu for their contributions and local expertise. Thanks also to Team eBird’s Brian Sullivan and NOAA’s Dave Nicosia for their insight into species distributions and weather respectively. Now, let the games begin.

Daily forecast maps are available here.

Olive-sided Flycatcher, San Clemente Island, CA, April. Photograph by Brian Sullivan.

Olive-sided Flycatcher, San Clemente Island, CA, April. Photograph by Brian Sullivan.

Olive-sided Flycatcher

Olive-sided Flycatchers should be on the move this week, especially across areas along the West Coast. An interesting species, Olive-sided Flycatcher shows a strong pattern of earlier arrival on the West Coast, followed by a later May arrival into the eastern and northern portions of its range. Widespread geographically, Olive-sided may be a species worthy of further scrutiny, as its taxonomy is still confused. In the West birds average larger, especially the bill, and this difference is most pronounced in birds breeding in southern California. But there are other differences not readily apparent in the museum tray: the above mentioned migration timing differences, and perhaps most importantly a subtle difference in the songs of Eastern and Westernbirds: listen carefully to the length and delivery of the middle note of the three-parted song. More study is needed to describe these differences, but keep an eye out across the West this week for returning Olive-sideds, as well as a careful ear for their distinctive ‘quick-three-beers’ song. Observers in the East should also be alert, but don’t expect to see Olive-sideds arrive there for another ~2 weeks.

There may be a brief opportunity for migration on Friday night over the Pacific Northwest, but this will be short-lived as northwest winds build in over the region into the weekend. A series of low pressure cells will move across the region next week, bringing unsettled weather in the form of thunderstorms. West winds over the Northern Rockies, followed by heavy precipitation later in the forecast period will limit the amount of migration through the region.

The California coast will be dominated by light northerly winds throughout most of the forecast period, but we can expect some light to moderate movement under these conditions, considering winds will be in the 5kt range and the atmosphere will be otherwise clear and warm. Of course these north winds may also cause more passerines and warblers to make their way up through the Lower Colorado River Valley as an alternate route north. Overall migration conditions improve as we move into the Desert Southwest and the Four Corners region, where light southwest winds should result in moderate to high levels of migration, with a notable increase towards the end of next week.

Look for widespread arrival of Western Tanager this week, as well as a slug of flycatchers including Western Wood-Pewee and Empids that occupy higher elevations. Vaux’s Swifts should make it to the Pacific Northwest as long as weather doesn’t hold them up. Shorebirds should be on the move in large numbers along the Pacific Coast.

Great Plains
The Great Plains will see some migration on Saturday night as a large Canadian high pushes down and brings southerly flow to the region. Birders should keep an eye out for some of the recently arrived Neotropical migrant wood warblers making their way into Oklahoma, Nebraska and the Dakotas. Birders there should also be on the lookout for both kingbirds and Scissor-tailed Flycatchers, as well as a slug of vireos. Mississippi Kite and Common Nighthawk should return to their breeding areas in the southern Great Plains this week, while swallow diversity should pick up in the Dakotas. A frontal boundary forming across southern Nebraska on Sunday night will limit northerly flow of these migrants and possibly result in some localized fallout conditions. The region clears again on Tuesday night and extensive migration is expected from Texas into the Dakotas. Birders throughout the region should be seeing more Neotropical migrants on Wednesday morning, after which migration conditions in the northern Plains begins to deteriorate. Expect migration in the southern Plains to continue into the end of next week.

Upper Midwest and Northeast
Southeast flow across the Upper Midwest will turn more southerly as high pressure moves south from Canada over the weekend. By Sunday morning we should see a strong interaction between the next cold front approaching from the west and the Canadian high now over the Mid Atlantic. This southerly flow will trigger widespread migration into the Upper Midwest from Sunday night into late next week. Because this southerly flow extends down into Texas, expect many Neotropical migrants to show up throughout the Upper Midwest during the forecast period. Birders in northeast Wisconsin and the central and western Upper Peninsula of Michigan should be on alert for fallout conditions on Monday morning due to thunderstorm potential, as well as concentrations along the northern and western shore of Lake Michigan as birds get pushed east on southwesterly winds. This could represent the first big push of neotropical migrants into the the Upper Peninsula. While winds should continue to be favorable across the region through mid-week, some storm activity moving into the Upper Midwest will likely shut things down locally. Conditions will deteriorate into late next week as precipitation becomes more widespread and winds turn northerly.

Birds will be grounded over the Northeast at least through Sunday as high pressure moves across the Great Lakes, pushing the low out of Eastern Canada. However, by Monday night conditions improve for most of the region and birds should be expected to move into the Ohio Valley again. This heavy push of migration should make Tuesday the first day that double digit warbler lists are likely in the Ohio Valley, with all but the last-arriving warblers (e.g., Mourning, Wilson’s, and maybe Blackpoll) making up the species mix. As high pressure moves off the New England coast on Monday night, expect things to really heat up with strong convection bringing birds out of the Southeast and into the region by Tuesday morning. Heavy precipitation along the southern Great Lakes and Ohio Valley could mean fallout potential on Tuesday and Wednesday mornings. Birders should keep an eye on the weather to see where they’re located in relation to the frontal boundary on Monday and Tuesday nights to determine whether to go north or south in anticipation of a fallout. Similar rainy conditions over the Coastal Mid Atlantic and New England on Wednesday could produce concentrations of migrants into Thursday morning as west winds convey migrants eastward.

Gulf Coast and Southeast
The Trans and Circum-Gulf expresses have been open for a few nights now and will continue to be throughout the forecast period. South to southeast winds will dominate the eastern Texas coast setting up favorable conditions for Circum-Gulf migrants to push northward, while southeast winds over the Yucatan will continue to funnel birds across the gulf and over Texas and western Louisiana. Given the easterly component to the wind, birders along the eastern Texas and western Louisiana coasts should be ready for migrants every day throughout the forecast period, and be on the lookout for species that usually travel over the eastern portion of the Gulf such as Bobolink and Blackpoll Warbler. Because of the relatively clear skies forecast until late next week, many of these birds may be pushing through to better habitat farther inland. Expect new arrivals to be well distributed across the landscape, so birders should be focusing efforts on inland spring migrant traps at least until the end of next week. By next Thursday expect some precipitation to set up along the eastern Texas coast, which could cause migrants to fallout on Friday.

As for Florida and the rest of the Gulf Coast, the strong easterly winds throughout the forecast period will mean only a light influx of birds into peninsular Florida, and whatever does come out of the Caribbean will be heading up the west coast of Florida to the panhandle, and coastal Mississippi, Alabama, and Louisiana. This subtropical jet may produce some interesting Caribbean migrants farther west than would be typical, so birders in Louisiana and Texas should be on the lookout for warblers such as Black-throated Blue and Cape May, and increased numbers of Blackpolls and Northern Parula by the end of the weekend.

Across the mainland Southeast we should see birds moving north out of the Gulf States tonight and into the weekend. As the next big high pressure system moves across the Mid Atlantic, expect migration to pick up full force through the entire next week. Fallout conditions increase by the end of next week as a strong front forms across the Tennessee Valley.

Posted 27 April 2012 by David La Puma of University of Delaware, and Brian Sullivan, Andrew Farnsworth, Christopher Wood, and Marshall Iliff of the Cornell Lab of Ornithology and David Nicosia of NOAA, on behalf of Team eBird and BirdCast.