Focus on Texas: April 2013, Migration, and the Big Day

Andrew Farnsworth The Cornell Lab May 02, 2013

Team Sapsucker made North American birding history on 25 April 2013, recording 294 species in a single, midnight-to-midnight day. More details are available here, but, briefly, the Sapsuckers pulled off a near perfect big day run because of a unique combination of the team’s skills, excellent scouting from Tom Johnson, Andy Guthrie, and Matt Hafner, assistance from many, many Texas friends on the ground, excellent weather conditions on the big day, and a forecast that allowed us to call our day a week in advance. And no flat tires . . .

There are several migration stories to tell about this epic big day, and the sections that follow below offer a brief introduction to discussion and speculation on this range of topics, some of which we hope to highlight in later stories. We will look at three scales – the hours before and during the big day, the days before the big day, and the weeks before the big day – to try to shed some light on why such a large number of species was possible in the single day. And finally, we will hear the words of some of our good friends on the ground in Texas who have had the good fortune to accumulate tremendous knowledge and perspective on migrants and migration on the Texas coast in the spring.

T-minus 12 hours, the Passing Cold Front

A fallout on any big day is an oft-discussed but rare occurrence, particularly when trying to choose dates for a big day many months in advance. Especially in Texas, a big day fallout is a huge game-changer for the number of species possible. This year, our timing could not have been much better. As much as a week in advance, Team BirdCast highlighted a likely fallout scenario for Wednesday 24 April, and the team planned its big day around this forecast event.

As the presumed day for our run, Thursday 24 April, approached, forecast models converged on an increasing likelihood that a strong frontal boundary would cross the coast and fallouts would occur as it pushed off the Texas coast. By Tuesday night, 23 April 2013, the forecast front was racing East and South across central Texas, having passed our Uvalde crew (See Fig. 1) and taking aim on our coastal Bolivar crew (Fig. 2). As this piece was falling into place, conditions over the Yucatan Peninsula and northern Central America were favorable for birds to take flight to make a trans-Gulf crossing, which they did.

Frontal passage

Fig. 1. The cold front passed Uvalde at about 4pm on Wednesday, pushing into the Gulf that evening.

Front above Smith Point

Fig. 2. The front moved off the coast and stalled. This image shows a substantial thunderhead in the background, with Smith Point in the foreground, approximately 3PM, 24 April 2013. Photograph courtesy of Delta Airlines.

The front moved off the Texas coast on Wednesday morning. Birds that had departed from Mexico and northern Central America on Tuesday night flew right into the strong storms, northerly winds, and poor visibility at the frontal boundary, which was sitting just off the coast by late afternoon. By Wednesday evening (see the synoptic map below) the front had stalled over the northern Gulf of Mexico. Birds were already pouring ashore along the Texas coast by late afternoon (see this checklist), and they continued to come ashore well into the evening (see this checklist from the following morning). The setup could not have been better for Team Sapsucker – a migrant fallout coming ashore hours before the Big Day, and strong northerly and northeasterly winds behind the front to keep migrants on the ground.

Wednesday Night

During the course of the Big Day on Thursday, 25 April 2013, high pressure pushed East across Texas. To the team’s benefit, this high pressure center’s position kept winds light during the midnight to dawn shift, even keeping substantial cloud cover and light rain in place between San Antonio and Uvalde, where the team could easily hear owls, nightjars, and other nocturnal sounds with ease. More important, the cloud cover, cool temperatures, and light rain kept most migrants present in the area on the ground. As the day continued, and as the team moved East, the position of high pressure also brought clearer skies closer to the coastal plain, allowing the sun to generate thermals, and putting a raptor movement in full swing by the time we reached San Antonio. Furthermore, the position of the high pressure center had implications for the remainder of the day (see the image below for the evening 25 April 2013 synoptic map) – calm winds prevailed for the afternoon and evening hours, making observation and listening easy. Moreover, the light winds allowed birds that had been grounded the previous day to take off, making for a wonderful chorus of flight calls by 9PM CDT, including Team Sapsucker’s #293 at about 10:30PM, Gray-cheeked Thrush.

Thursday Night

T-minus 96 hours, downed migrants and lingering winterers hang on

The passage of a front and a resulting fallout in the 12 hours prior to beginning our big day was key for the team, without a doubt. An influx of new trans-Gulf migrants, and numbers of them at that, was a dream come true. But also important in considering the Sapsucker’s total list is the number of lingering wintering species still present in large numbers. A likely explanation for the numbers of lingering winterers focuses not on the conditions in the hours before the big day, but on the conditions over the week leading up to the big day and even the weeks leading up to the big day.

Almost a week before our run, another strong cold front had passed through Texas and moved into the Gulf of Mexico. The passage of this system upset the typical flow of migrants from points farther south into the US, creating marginal conditions farther South for movements in the days that followed. Additionally, any movements that did happen favored overland, circum-Gulf movements. At the same time conditions in central Texas and other parts of the state were not favorable for birds to take off once they arrived on site, so species like Hudsonian Godwits at Mitchell Lake, lingering ducks, and wintering sparrows and Tree Swallow tended to stay in place. So, between a strong front on 18-19 April, another on 24-25 April, and numerous days of marginal and semi-favorable winds over the Gulf of Mexico and northern Central America, there was a recipe for birds to linger, migrants to accumulate, and migrants to get grounded. But there is even more to the story at an even coarser, longer time scale . . .

T-minus 4 weeks, Battered by fronts, or why has April 2013 produced so many fallouts?

Taking the story of fallouts, arriving migrants, lingering winterers, and downed migrants to a slightly coarser scale, we can think about the spring of 2013 and why so many fallouts and lingering winterers were part of the equation. We think that the Jet Stream may play a substantial role in any explanation, and the story goes like this . . .

The weeks prior to the big day saw the jet stream take on unusually contorted shapes (see this excellent description by Dr. Jeff Masters at Weather Underground). During periods when these oddly shaped Jets occur, low pressure systems and frontal boundaries can move far to the south, passing over the Gulf of Mexico and into the Caribbean, as cold air masses and high pressure dominate over the Eastern North America (and Greenland!). In years where Jets get contorted, and more cold fronts reach the Texas coast and push into the Gulf of Mexico, more fallouts should be the expectation (dissertation anyone?). And the overarching explanation for why the Jets get contorted in the first place? Birdcast (and others!) suggest that our old friend that brings us Eastern Promises, the North Atlantic (and Arctic, AO) Oscillation (NAO) . . . In years with strongly negative NAO and AO indices, weaker, meandering, and contorted Jet Streams tend to be the norm.

Furthermore, when we look back to April 2012, we see a different pattern of frontal passages and temperatures to contrast with April 2013. A nice summary explanation can be found here. The graphic below, albeit from the month of March, illustrates the dramatically different patterns between the two years. It highlights an exceptionally warm eastern US in 2012, one in which the central US had just experienced an unusually warm winter. The pattern continued into April in many areas, and warm and blasting southerly flow was generally the norm in Texas. The pattern of 2013 has been dominated by a much different set of conditions, in particular the numerous strong frontal passages during the month of April after a substantially colder March. Furthermore, the Jet Stream was a much different beast in 2012, locking into more typical patterns rather than meandering and contorting widely over North America. And of course, 2013 has seen a very strongly negative NAO index, with extremely high pressure over Greenland and the North Atlantic, which has meant a very different look to the Jet Stream for spring 2013!


Some perspectives on fallouts . . .

Teams BirdCast, eBird, and Sapsucker have many friends in Texas, and there are many invaluable perspectives that they have shared with us from their experiences on the ground in this fallout and from fallouts in previous years. Rather than summarize, we asked them their opinions:

From Mel Cooksey: “This storm just socked in and stayed with us. The 24th and 25th were just low-visibility, low-sky rainy, windy overcast days, with birds continually flying over and dropping in to every patch of green. This is actually a different experience than I have seen in 25 years here. We have had similar conditions in April, but not as bird-productive as this one. My notes are sketchy on weather, but May 3-4-5 ’94 was one of the best fallouts in my memory, with similar volume to this one, if memory serves. That was NOT a spectacular weather event; sort of a mild front, really. But the birds fell out of the sky. April 25-26 92 was a strong fallout but was localized a bit, I think. Our species list was about the same as this storm, but numbers of the thrushes, grosbeaks, buntings were higher with this storm. March 27-28, 1992 was a storm that really produced a lot of birds for 3-4 days, and helped us to understand early arrival dates of lots of species. It was sort of localized, but nasty on the barrier islands. April 26-27, ’97 was really fun birding, mostly series of spotty thunderstorms that produced lots of good birding without a major mortality factor, as I recall.

From Willie Sekula: “It seems like each major fallout has its own ‘flavor’ so to speak.  The one last week (24-26 April) seemed to really have grounded thrushes, grosbeaks and orioles.  Warblers were certainly grounded but not in some of the numbers that you would expect.  I was wondering that the larger and stronger fliers like the thrushes, orioles and grosbeaks might not have stood a better chance of making it to land rather than the warblers.  The winds were really strong for late April (and that seems like it’ll be repeated with this next cold front due tomorrow).  I don’t remember northerly winds being that strong for such a length of time in late April . . .”

From John Arvin: “My major thoughts were how amazingly similar the events were to the last really amazing fallout I had seen. That one was under the same conditions, on about the same dates, and with similar effects on birds, but it took place April 21-24, 1981! I experienced two days in Corpus Christi and two in the Brownsville area (but not on South Padre Island, the epicenter of this year’s activity). It was under tour conditions (with Rich Stallcup) so we couldn’t spend as much time as we would have liked chronicling the fallout.

A cold front arrived in Corpus the evening of April 20 with a hour or so of hard rain tapering off to light rain that was still going on the next morning. We arrived at the entrance to Packery Channel County Park around first light and sat in the van watching warblers of several species working over the smashed insects on the radiator of Rich’s van. When the rain slacked off we got out and huddled in the lee of the live oak covered dune that marks the entrance to the park. The lee side was covered with birds. We could reach out and stroke Eastern Wood-Pewees and Acadian Flycatchers. Soon the participants were combing the grass for small insects which they then fed by hand to the flycatchers. The ground was covered with birds and it was tough to avoid stepping on them. A gorgeous male Cerulean Warbler hopping around on the ground hopped up onto my toe for a while.

A few amazing memories stand out – Black and Yellow-billed Cuckoos sitting shoulder to shoulder, 2000 estimated Rose-breasted Grosbeak males throughout the day, a Worm-eating Warbler and a male Scarlet Tanager having a tug of war over a small frog, hundreds of dead and dying swallows (mostly Cliffs) that piled up smothered the bottom layers, a Chimney Swift “stripe” up the lee side of a big tree trunk in Sarita and many other amazing tales. I stopped telling this story to birders years ago because everyone thought it was a crock.

I think the conditions that produce spectacles like this come together in time and space extremely rarely. A late very strong front with an initial squall line followed by two or three days of over-running cloudiness and light rain with cold temperatures and moderate north winds are required.”

Numerous other accounts generally agree with what John, Willie and Mel have highlighted, in that this system was strong, uniquely positioned, and a rarity in terms of the magnitude and seasonal timing combination.

. . . and a continuing wake-up call for bird conservation

As amazing as these fallouts can be, they can be devastating for the birds. In systems as severe as the 24-26 April frontal passage, many tired migrants, particularly smaller bodied birds, may come ashore exhausted and may get downed into the Gulf of Mexico. And those that do make it ashore face the perils of diminishing coastal stopover habitats, increased predation from cats and waiting gulls, and more structures and vehicles with which to collide. So, above all, perhaps the most important perspective to remember about the big day and the fallouts from this year is the one that inspired the big day in the first place: bird conservation. Tired migrants need stopover habitat at the coast, when they arrive, for food and shelter, and several groups in Texas in particular have worked hard to save some of the last areas along the barrier beaches. Furthermore, projects like eBird and BirdCast provide unique insights and databases we can use to monitor the pulse of migration, habitats, and populations. Teams BirdCast, eBird, and Sapsucker urge you to support organizations like Houston Audubon Society and donate to projects like eBird and BirdCast to continue saving habitats, promoting good conservation practices, and above all, promoting good science to help us understand these amazing occurrences.