North on the Wing

by Bruce M. Beehler

  The little crew was intrepid, working in a habitat with strong winds, relentless sun, swarming mosquitoes, and venomous snakes. Their long days started well before dawn, which sometimes brought the excitement of trembling nets full of new arrivals and other days only the frustration of nets filled with dried leaves blown off the sheltering trees. Each hour the team checked the nets, mounted along narrow pathways cut through the scrub. Every netted bird was carefully removed, placed in a cloth holding bag, and brought to the project tent for banding. All birds were weighed, measured, and studied for fat deposition, age, and sex. From some birds, the team also collected a small blood sample to check for blood parasites and plasma metabolites that could reveal physiological condition. The team also searched the birds for ticks, which they preserved for study by taxonomic and epidemiological experts. After this meticulous treatment, the team released the birds unharmed to continue their northward journey.

  This banding camp operates for nine weeks each spring, and by season’s end the team knows all the resident birds of Mad Island as well as the passage migrants that have migrated through. The team told me that the main benefit of working on the banding project is the unlimited access that participants have to the Mad Island coastal prairie environment, with its rich diversity of wildflowers, snakes, frogs, butterflies, mammals, and birds.

  During my second morning at the banding camp, a low cloudbank hangs on the coast. A Texas Spotted Whiptail, a nine-inch lizard with green dorsal stripes and small, pale spots on its flanks, searches for a patch of warm sand on the sandy access track to the station. These lands have many reptiles and amphibians as well as birds. This one speeds off in a colorful flash upon my approach.

  The first bird netted this morning was a Nashville Warbler. Tim Guida carefully banded and measured it, a process that took about five minutes. Done, he extended his arm with his hand lightly enclosing the small yellow, olive, and gray bird, then slowly opened his fingers. The warbler lay on its back for a couple of seconds before sensing its freedom. It quickly flicked its wings and darted off to a low bush a few paces from the banding tent. It preened for a few moments, collected itself, and flew strongly over the canopy of the scrub and out of sight, its aluminum band glinting in the sunlight. The Nashville Warbler is a boreal forest breeder on its way not to Tennessee (despite its name) but up the Mississippi Valley to the North Woods. This bird, and millions like it, would be preceding me northward in the weeks to come. I hoped to encounter more Nashville Warblers singing on their territory in northern Ontario in mid-June.

  As the sun rose toward its zenith, the glare off the sandy expanse of the clearing grew intense; I squinted out from the banding tent over the narrow shipping canal to the expanse of Matagorda Bay, where dredge boats were harvesting oysters and flocks of gulls hovered overhead in hope of snatching something edible. The southwest wind started to build until, just before noon, Guida decided to halt netting. An inevitable challenge of working on the coast is the onshore wind that can blow steadily off the water, presenting problems for bird netting even on otherwise pleasant days. Windblown leaves tangle in the mist nets, which themselves lurch around and snag in vegetation. Because they are somewhat fragile, the nets can tear, making them more visible to birds and thus less effective at catching them. Guida instructed the team to close the nets, which they secured with colorful strings.

  Nets closed, the team and I went out to explore the preserve, walking on sandy roads through the property and visiting Skeeter and Pintail ponds. We saw many resident marsh birds but were surprised by what we found far from any woods: two male Orchard Orioles and a Wood Thrush, holed up in a single isolated shrub. This is the type of place an exhausted songbird migrant ends up when it descends into an inappropriate habitat after a long trans-Gulf flight. At least these birds had made it to terra firma, done with their crossing of the open sea.

  A pair of White-tailed Hawks put on an aerial show for us over the low grassland—the climax of the afternoon. They have the bulk of a Red-tailed Hawk but unmarked all-white underparts, a gray dorsal surface, red-brown shoulder patches, and a broad white tail marked with a neat black subterminal band. The species flies with its wings tilted upward, distinguishing itself from a distance by this unusual silhouette. This big nonmigratory tropical raptor reaches the United States only in the coastal prairie of southeastern Texas, but its global range extends all the way to southern Argentina. Here in southeastern Texas, it is a local coastal prairie endemic—one of those species confined to a tiny corner of the country. For that reason, few American birders ever see it.

  The next morning, Cohen and the preserve manager, Steve Goertz, continue my behind-the-scenes tour of the preserve. The coastal prairie at dawn is very birdy. a pair of Crested Caracaras hang out in a low tree that held their nest last year. Strongly patterned and wary, the pair makes off before we get close enough for a photograph, exhibiting in flight their strange silhouettes, with long necks and steady, rowing wingbeats. Several coveys of Northern Bobwhite quail race across the dirt track in front of Goertz’s truck as we slowly rumble over the prairie, and a Loggerhead Shrike perched on a low fence line speeds off with whirring wings that flash black and white in the morning sun.

  The relative abundance of Northern Bobwhites and Loggerhead Shrikes here in southeastern Texas was a pleasant surprise because they have disappeared from virtually all their former range in the eastern United States. Why are they common in southeastern Texas? Biologists think it is due to the abundance of invertebrate prey available here for these two open-country birds. Solutions to large-scale conservation problems can arise in environments such as this one, where a juxtaposition of beneficial environmental factors and benevolent human interventions produce a positive result. Yet finding such solutions is a matter of focused trial and error. No one had ever restored a Texas coastal prairie before Goertz and his small team initiated their program, deploying selective grazing and judicious use of fire and herbicide to control tenacious invasive plant species. The restoration of Mad Island as a native coastal prairie will require decades of effort. But by saving this land from development, the Nature Conservancy has already taken a major step for its protection.

  The highlight of the third morning at the preserve was a pair of Upland Sandpipers that flew up from a patch of short grass, giving their weirdly musical, trilled, rising and falling flight song. These grassland specialists had recently arrived from their wintering grounds in the pampas of Argentina. Because of declines in grasslands, eastern birders don’t get to hear this song much anymore; today the species is mainly found in the prairie country of the northern Great Plains.

  Upland Sandpiper

  THE NATURE CONSERVANCY’S PRESERVATION OF PRIVATE LANDS

  Since its founding in 1951, the Nature Conservancy (TNC) has focused on preservation of private lands in the United States. To date, TNC has ensured protection for more than twenty million acres of private lands and managed these properties to maintain or enhance their ecological value. Because of its strong national reputation, TNC often receives donations or bequests of private land of significant natural value, and the Runnells family’s land was one such property. While donations such as this one are an effective method of achieving conservation if resources are available, long-term costs are incurred in the maintenance and management of private lands. Sometimes TNC simply purchases land outright and then passes the property to a state or federal entity to carry out long-term management.

  Aside from the purchase and maintenance of property, TNC has also pioneered conservation easements on private properties that both benefit landowners and ensure perpetual protection of natural values. Easements enable land managers to achieve targeted objectives while keeping land under private ownership, and they can help conserve tracts of forest, protect water quality and scenic vistas, and create wildlife habitat. Typically, TNC purchases easement rights from a landowner and thus achieves a conservation “win,” while the landowner receives a tax benefit. The United S
tates has a large network of local, state, and national protected lands, but by adding a portfolio of private lands, TNC has expanded the reach of conservation across the country. Today more than 40 million acres in the United States are covered by private conservation agreements, compared to 10 million acres under state protection and 170 million acres conserved by the federal government. Private protection is particularly important for preserving lands with very specific conservation values that otherwise aren’t protected by the governmental sector—as is true of Mad Island’s critically endangered Texas coastal prairie.

  The 2015 netting season at Mad Island lasted from mid-March to mid-May. The team banded 1,972 individual birds of 81 species, including local residents and Neotropical migrants. The season’s highlight was a big arrival of Dickcissels, which for several days perched atop virtually every bush, plus rare species including ten Golden-winged Warblers and an out-of-range Western Tanager and Yellow-Green Vireo. Overall, the team observed 230 species of birds during the spring. The 2015 season was memorable to the field team because it was particularly wet, generating abundant wildflowers and many Cottonmouth snakes but no huge flights of Neotropical migrants. No matter the spring weather, though, the team collected another year’s worth of spring migration data. As results from more years become available, bird-banding projects such as the one at Mad Island will help us to refine our understanding of northbound songbird migration under various weather regimes and wind patterns.

  My stay at Mad Island gave me a small taste of the songbird migration to come. I learned about the coastal prairie and saw first-hand private lands conservation in action. I was now headed up the coast of Texas to another birding hotspot, at a time when birds would start flooding into the coast.

  THREE

  The Coastal Oak Woods of Texas and Louisiana

  MIGRANT MAGNETS

  Early April 2015

  Northern Parula

  All of a sudden a warbler starts and stops. All of a sudden it flashes from branch to branch, peers under leaves, snaps up caterpillars, darts on again.

  —EDWIN WAY TEALE, North with the Spring

  In the hour before dawn, a Great Horned Owl hoots its low, cadenced five-note series close to the Mad Island lodge. As sunrise approaches, fog cloaks the prairie, and dew soaks the grass and my tent. The winds are light this morning, so work will go forward at the banding station. There has been no big arrival of Neotropical migrants, and by midmorning, I’ll say my good-byes and head three hours northeast toward my next destination: High Island, Texas. Perhaps a big pulse of Gulf-crossing migrants will show up there in the next few days.

  High Island is a tiny coastal community that sits atop a salt dome amid a broad expanse of saltmarsh in the easternmost corner of Texas. It is isolated from I-10 and the strip-mall town of Winnie to the north by the shipping channel of the Intracoastal Waterway, which carries barge traffic between industrial facilities in southern Louisiana and coastal southern Texas. This channel also passes in front of the Mad Island banding camp, three hours to the southwest.

  Birding and fishing are the primary attractions of High Island and its environs; its small downtown includes only a single motel and a gas station/convenience store, both crowded in spring with birdwatchers who come here to check out arriving migrant songbirds in the woodland reserves, to visit the local waterbird rookery to see displaying egrets and spoonbills, to wander the adjacent Bolivar Peninsula to spot birds of beach and estuary, and to visit adjacent Anahuac National Wildlife Refuge for marsh and open-country birds. For a few weeks each spring, this corner of Texas produces some of the best birding on earth.

  Like Mad Island, High Island is not a true island surrounded by water. Instead it’s a small wooded rise ringed by marshlands, its uplands beloved by birders for the oak woodlands that lure passing songbird migrants in spring. The songbirds arrive at High Island after their overwater crossing and descend into the community’s woodlots to feed, drink, bathe, and regroup. Winding sylvan trails in the small reserves allow birders to approach these normally elusive birds up close.

  High Island is diminutive and its woodland reserves are tiny as well, yet they can attract remarkable concentrations of songbirds. The community features five private woodland sanctuaries owned and operated by the Houston Audubon Society and the Texas Ornithological Society, each of which offers critical food and shelter to migrating birds on their way north. They are the focus of an annual springtime pilgrimage by birders from all over North America, who come in hopes of seeing a songbird fall-out.

  SONGBIRD FALL-OUTS

  Whereas the Mad Island coastal woods attract both trans-Gulf migrants and those traveling north along the eastern coastline of Mexico, most songbirds arriving at High Island have flown over the Gulf. Many of them depart from the Yucatán Peninsula in southeastern Mexico, about six hundred miles south-southeast of High Island. Some have already flown there from Amazonia, Colombia, and various parts of Central America, journeying in jumps that in some places required them to travel over the Caribbean. On the Yucatán, the migrants feed, rest, and wait for benign southerly winds and fair skies—conditions favorable for a flight north over water.

  When conditions on a spring evening are promising, these birds rise into the sky and fly north, eventually reaching a cruising elevation of several thousand feet, depending on where they find favorable winds. Some species apparently fly north in small groups, staying together for the long flight. They keep a fixed course and travel all night, not making landfall on the U.S. mainland until late in the afternoon of the following day: a flight of some fifteen to eighteen hours. Those crossing the Gulf include not only Neotropical songbirds but also birds of various other lineages—herons, ducks, shorebirds, cuckoos, and more. Between mid-April and mid-May, rivers of birds pour northward across the Gulf, millions and millions of them heading toward the U.S. coast. They are not attempting to arrive in a specific spot on the U.S. mainland; nor do they need to. Examining a map of the lands surrounding the Gulf shows that a bird departing the Yucatán and flying generally northward will eventually make landfall somewhere, no matter how far off course it strays, because there is Florida to the northeast; Louisiana, Mississippi, and Alabama due north; and Texas to the northwest. This long arc of coastline can generously accommodate the migrant birds no matter which way the winds may carry them.

  If the weather remains fair and the winds are following, the birds have an easy flight, and, upon reaching land, most keep flying northward until they reach the extensive bottomland forests of the mainland interior. If, on the other hand, the winds turn or rain or thick fog disturbs the birds’ northward travels, they may have difficulty making it to the coast. On those days, the exhausted migrants tend to descend at the first sign of land and head straight for the nearest coastal woodland patches. This is when places such as High Island prove both vital for the birds and exciting for birdwatchers.

  The most extreme bouts of contrary weather create what is called a fall-out, in which massive numbers of northbound birds literally fall out of the sky to land on the coast. A fall-out—while not necessarily killing birds—is a taxing event for them. Each time a migrant songbird heads north from the Yucatán, it is taking a chance. It makes its move because of favorable local weather conditions, but it cannot predict what weather may occur en route. A strong cold front could be heading southward out of the Great Plains. Or a band of thunderstorms might blanket the Gulf Coast. Both spell trouble. Birders watching from beaches during bad weather have seen migrants moving heroically just above the wave tops, fighting a headwind to cover the last few hundred yards to solid ground. Some individuals drop into the waves just short of their destination; other birds make it to the beach and then expire from hypothermia and starvation. Fortunate others labor to shore, land in a shrub, and immediately begin refueling on tiny gnats and other prey.

  Offshore observers on oil-drilling platforms have reported thousands of small songbirds flying into headwinds but making virtually no prog
ress. Some stopped and rested on the platforms’ superstructure, but most continued on without pausing. It seems that the birds are focused single-mindedly on making it to the coast. Luckily, such catastrophic events have been seen only rarely by platform-based observers. On most days (and nights), the migrants move at high elevations over the rigs and continue northward, making their crossing successfully.

  Why do at least sixty-five species of Neotropical migrant songbirds take the trans-Gulf route rather than the more circuitous one around the bend of the Mexican coast (chosen by seventeen of the species)? Despite the hazards, the overwater route must be the more efficient and advantageous one. A migrant takes the overwater journey across the Gulf because it gives the bird a leg up in the race north to claim a breeding territory and optimize, over its lifetime, its production of offspring, contributing to the gene stocks of future generations. The unsympathetic hand of natural selection drives the evolution of bird behavior, including the innate selection of particular migratory pathways.