Exploring the wonders of spring bird migration.
By Noreen Damude
In tune with ancient rhythms, the ruby-throated hummingbird prepares for the long trek to northern breeding grounds as early as February. He begins to feed more vigorously now, laying down gobs of fat just under the skin. He zips and dashes from flower to flower with a special urgency, spending much less time preening and sitting still. In a matter of weeks, he puts on twice his meager weight. A hummer butterball, he is ready to depart, carrying his own high-test fuel in the form of fat. Following trails of flowering plants, he makes his way up the Yucatan peninsula. As the great mass of southerly winds move in, the time is right. Solitary, flying by dead reckoning, he launches himself into the night sky, hell-bent for the Upper Texas Coast. Six hundred miles over a black, killing sea, he zooms across, wings buzzing at a mind-boggling rate of speed. It’s early March. Many of his fellow ruby-throats will pass through Texas on their way further north and east. Some will continue on as far as Canada. Austin, almost at the western limit of its southern U.S. range, hosts a few breeding ruby-throats, with many farther east. During the winter, ruby-throated hummingbirds share pine-oak-fir forests with resident birds in Mexico and Central America. There they forage in the company of masked tityras, golden-browed warblers and cinnamon-bellied flowerpiercers.
The Rite of Spring:
With their myriad adaptations for movement in water, on land and in the air, birds are, in Walt Whitman’s words, born “to match the gale, to cope with heaven and earth and sea and hurricane.” Heeding the urges of spring, a host of feathered wayfarers heads north, reenacting the age-old drama of seasonal migration. Spring is a great time to head for the Upper Texas Coast to view the many birds arriving, leaving or just passing through, as they fly from their Neotropical wintering homes to their northern breeding grounds. Birders call these spring flocks “waves” because of the way they roll across the landscape. Typically in late afternoon, flotillas of birds move in from the Gulf, flying over beach and field to dive suddenly into the protective cover of the welcoming trees. Catching the biggest waves in spring, when the world becomes a riot of renewal, movement and song, defines the annual rite of spring for birders who head for the stands of live oak and hackberry along the Upper Texas Coast. ¶ Riders on the Wind: When the axis of the earth inclines toward spring, millions of birds take to the skies, following the southeasterly winds. Well-spaced battalions lift off soon after dark from the Yucatan Peninsula and from coasts farther south — the grand passage is underway. The vanguard of songbird migration may reach the Gulf Coast as early as March and continues to surge, peaking in April, and trailing off by early June. The birds are not misled, those that fly by day — ducks, geese, cranes and hawks — believe in the zenith of the sun; it’s written in their germ plasm. Those that fly by night rely on a redundancy of cues, from celestial constellations patterned against the Pole Star to heady resonances of infrasound and the geomagnetic field. Even the sense of smell may guide a few. The sweep and drama of bird migration in the Western Hemisphere shifts endlessly across distance and season. Some that spent the winter in Texas, such as northern pintails, hermit thrushes and Lincoln’s sparrows, will leave for the northern U.S. and Canada to breed. Others that departed for Latin America last fall, like yellow-billed cuckoos, scissor-tailed flycatchers and indigo buntings, will return to Texas to breed. Still others, like buff-breasted sandpipers, scarlet tanagers and rose-breasted grosbeaks, may land here to refuel before continuing on their way farther north. The boldness of their annual hegiras never fails to stir us, reminding us again of that cycle of beginnings and closings we call a year. ¶ Meet the “Flying Tigers”: While by no means an exhaustive list, this quick set of cameo portraits of Neotropical migrants reliably seen along the Texas Coast offers a colorful smattering of what lies in store for birders who celebrate the grand passage of spring migrants that grace our state come spring.
The resplendent male rose-breasted grosbeak is unmistakable with his bold black head and back, heart-shaped, rose-colored breast, white underparts and large triangular-shaped bill. Long-distance migrants, grosbeaks pass through Texas on their way north to breed throughout much of eastern North America. During migration, they may come down in any wooded or semi-open area where they favor leafy woodlands — often staying out of sight among the treetops. Sometimes, they hover to glean insects from foliage or fly out to catch insects in midair. They also eat seeds and small fruits, especially ripe red mulberries that abound upon arrival on High Island. Nocturnal migrants, they begin to move from their wintering grounds in Central and northern South America relatively late in the spring. Birds stray widely during spring and fall migration, appearing well west of their normal range. Sadly, rose-breasted grosbeaks have been declining over certain portions of their breeding range, presenting a challenge for conservation biologists to stem the tide of their dwindling numbers.
A flaming black and orange ember flickering through the leaves on a shaft of golden sunlight announces the arrival of the beguiling American redstart. High in a live oak in Sabine Woods, he darts out like a flycatcher to snare a passing bug, misses his target and abruptly flutters down through the sun-spangled leaves, spreading his wings, fanning his tail and flaunting his brilliant attire. Down he comes like a tropical butterfly, only to swoop upward suddenly and perch jauntily on the overhanging limb. One of the most dainty and winsome of all the warblers, the American redstart, also called the forest-firetail, is a “butterfly” of a bird, the sole representative of his genus. Doing the “hoochie-coochie,” flashing his tail and drooping his wings, the male is a blithe flash-dancer, more like a flycatcher than a wood warbler. Breeding over much of North America, birds nest in open deciduous and mixed second-growth woodlands. Redstarts winter throughout Central America, from southern Mexico south to northern and western Amazonia, including the West Indies, where they frequent humid lowlands. A medium- to long-distance migrant, come spring, American redstarts travel in small flocks at night, moving north on a fairly broad front across the Gulf rather than following the Mexican coast. Many first-year birds remain in the Greater Antilles throughout the year. In Texas, American redstarts migrate through all kinds of woodlands and undergrowth, showing up as well in city parks and gardens. An expected annual nester in East Texas, their delightful showboating is a joy to behold.
Just as over-water migrants must find land, so desert travelers like the Townsend’s warbler — a bird adapted to high, cool mountain forests — must find a suitable haven when daylight breaks. Desert springs, cienegas and seeps, shining green in the morning sun, fit the bill perfectly. Like shorebirds hop-scotching from one stopover site to another, northbound songbirds must find suitable habitats at every stage of their trip. This is relatively easy in the East where forests are widespread, but in the Southwest, wooded habitats are few and far between. Like a swimmer in a strong current, a bird may be pushed off course by stiff cross-winds. Such drift helps account for the puzzling appearances of western birds well east of their normal flight path. High Island periodically hosts a few of these dapper western strays, keeping birders who are expecting to see black-throated greens on their toes.
Looking distinctly tropical in his flaming orange-and-black attire, the Baltimore oriole fits just as well into the tangled ecology of the Neotropics as he does in the oak woods of the Midwest. On their wintering grounds, they frequent semi-open forest canopy, shrubby vegetation along edges and second-growth woodlands. In Costa Rica, they are frequently seen in mixed-species foraging flocks, sharing trees with toucans and parakeets. Here they gorge on nectar from blossoms of the beautiful tabebuia and coralbean trees, a marked departure from their usual fare of fruits and insects favored on the breeding grounds. Shuffling sideways to reach a flower, they grasp it at its base, twist and tug to pull it free then sip the nectar from the tubular flower — sweet cheats in terms of pollination. Birds remain only four months in the temperate zone of North America; the balance is spent migrating or in its nonbreeding range, which stretches from Mexico to northern Colombia — nearly seven months in the tropics. Baltimore orioles migrate at night in flocks of 25 or more. Those fortunate enough to witness a mass arrival never forget the electricity of saturated color falling from the skies.
When you think of champion long-distance trekkers, the Hudsonian godwit, American golden-plover and Arctic tern immediately come to mind. Traveling thousands of miles a year, the two shorebirds are strong, robust creatures with powerful wings to propel them long distances over water. Arctic terns are graceful “wind-catchers,” able to land on the water and rest during their epic journeys from the Antarctic to Arctic shores. An unlikely contender for the prize in its size category, weighing not much more than a first class letter, is the blackpoll warbler. Hardly looking like a transoceanic traveler, this diminutive black-and-white songbird is renowned for its Promethean voyage to its South American wintering grounds. In late August, blackpolls that nested in Alaska begin to head east across the boreal forests of Canada to the Maritime Provinces and northern New England coast. While a few birds of the year may hug the shore, most blackpolls strike out south over open ocean. They pick a night with a brisk, northerly tailwind after the passage of a cold front to take off, leaving soon after dusk. For the next 40 to 50 hours, depending on the winds, the tiny songbirds fly at an altitude of more than 5,000 feet over the western Atlantic, wings buzzing at a dizzying 20 flaps per second. As they round Bermuda and the Greater Antilles, they trace a curve, guided and abetted by the winds. When they reach Bermuda, the northwesterlies fail and the nearly exhausted migrants pick up the friendly subtropical trade-winds that ferry them in a southwesterly direction towards South America. Most make final landfall along the coast of Venezuela — an over-water trip of nearly 2,000 miles — with no rest, no water and no refueling. The trip requires a degree of exertion not matched by any other vertebrate. For a human, the metabolic equivalent would be to run 4-minute miles for 80 hours, note ornithologists Tim and Janet Williams. “If a blackpoll warbler were burning gasoline instead of its reserves of body fat, it could boast of getting 720,000 miles to the gallon!” Most other warblers travel between 200 and 400 miles each night during migration, with stopovers to fatten up between flights. Despite these unimaginable hardships, blackpolls are fairly numerous “eastern” warblers in the spring along the Upper Texas Coast. The fact that they make this journey each year of their adult lives is truly one of the miracles of the avian world. In spring they opt for an overland route up through the central and eastern U.S. Zigzag, illogical, far-flung routes are not the paths of biological necessity, but more often the fruits of tradition. Birds do not always fly straight as an arrow from winter to summer territories, and they don’t always take the same route both spring and fall. For the blackpoll, the unspeakably difficult elliptical migration has worked best to ensure this species’ success.
Common breeders in the eastern half of Texas, indigo buntings arrive en masse in spring along the Texas Upper Coast, ornamenting trees, shrubs, lawns and roadsides during fall-outs, like shiny Christmas bulbs. They made it. The indigo-blue males, looking black at a distance, sing boisterously from telephone wires, tree tops and fence posts to celebrate. Flocks of exhausted migrants feed ravenously for seeds and insects on the ground near brushy woodland patches. Probably more common today than when European settlers landed on American shores, indigos seek out woodland edges and riparian areas to set up nesting territories. Birds winter in Mexico and Central America, where they frequent similar brushy second-growth habitats. Interestingly, indigo buntings played a critical role in helping scientists understand celestial navigation in migratory birds. Most migrate at night in both spring and fall, navigating with uncanny precision by the stars. Never leaving the Northern Hemisphere, they can always see the North Star, unlike trans-equatorial migrants that winter in South America. Studies have shown that indigo buntings focus on the position of the North Star in relation to the Big Dipper to guide them accurately during their flight.
Migrating by day is not the sole monopoly of larger birds like hawks, cranes, geese and cormorants. Because aerial foragers, such as martins, swallows and swifts have no need to stop to periodically refuel, they feed continually on the wing as they head north. These are the birds most often seen during migration. Swallows in an unending stream course low along our reservoirs, levees and pastures as they move northward. Purple martins are the shock troops of the invading migratory invasion. What the American robin is to New Englanders — a welcome harbinger of spring — the purple martin is to Texas, arriving as early as the end of January at the state’s southernmost tip. Brave scouts face hard freezes and killing sleet as they proceed north to claim traditional man-made martin houses and hanging gourds. Many perish as insect food is squelched during extended cold snaps. But the risk is worth it. Claiming traditional martin houses makes all the difference in assuring reproductive success — continuing the genetic legacy of the scout’s clan.
For further information on the miracle of bird migration, see Living on the Wind by Scott Weidensaul; Ornithology by Frank Gill; Gatherings of Angels: Migrating Birds and Their Ecology by Kenneth P. Able; Bird Migration: A General Survey by Peter Berthold; and Bird Migration by Robert Burton.