Ever seen a river turn from freeze to fire? Or watched a blue-sky morning blizzard?
At dawn, the Susquehanna River, some 40 miles above where it widens into Chesapeake Bay, appears littered with ice downstream of us, where it braids through forested islands of the Conejohela Flats, near the village of Washington Boro, Pa.
The weather is a face-cracking 10 degrees, enhanced by a stiff northwest wind, as sunrise slops over the eastern hills and splashes into the river corridor.
As the light turns up, so does the volume from thousands upon thousands of big, white waterfowl, tundra swans and snow geese, staging here on their northward migrations from bay country. The swans, piping wild notes reserved for creatures with meter-long windpipes, mass in luminous drifts along the lees of the islands. Snow patches on the banks look drab by comparison.
Some pairs of swans stretch and arch and preen and bob their heads -- classic courtship and bonding behavior. Is it spring fancy? Or merely efficiency, getting the preliminaries out of the way now?
For they must haul their 20-pound bodies as far as 4,000 miles to reach Alaskan breeding grounds, where the brief summer demands reproduction and rearing of the young without dalliance.
Doomed are the young swans, or cygnets, that cannot manage the odyssey back to the bay, and North Carolina's sounds, by mid-September, when the Alaskan tundra ices over again.
Here on the Susquehanna, the light builds, and to the swans' obbligato, snow geese erupt like solar flares off the river's cold surface, great, packed flocks sparkling skyward. Then they drift back down, a brilliant snowstorm against the dark-shadowed backdrop of Turkey Hill, a towering outcrop of half-billion-year-old rock downstream, where the river bends sharply around the Lancaster County shore.
The snow geese are an unexpected bonus for us. It was the mid-March massing of the swans we had come to see; but locals said that just in the last few years, as many as 100,000 of the snows also have been staging in the region.
Put it on next year's calendar, because the spectacle passes swiftly. By now, a river of swans, strung out hundreds of miles long, has begun flowing out across Lake Erie, the marshes of the upper Mississippi, through central Canada to the MacKenzie River delta, to the rim of the frozen Arctic Ocean.
Because we have known for a long time that birds go north in summer, and south in winter -- and because we know the end points of these journeys -- people wrongly assume that we understand everything in between.
But with the tundra swan, as with many other migratory species, important questions go unanswered: How high and fast do the fliers go? How often do they stop to rest? Where? Is this stopover habitat, so critical for food and rest, being lost?
It was a team of Marylanders -- aided, ironically, by a tragic plane crash -- that first began to unravel the mystery of the swans' epic journeys to and from the Chesapeake.
A United Airlines Viscount, flying just over a mile high above Ellicott City, on Nov. 23, 1962, collided with a flock of swans, knocking a horizontal stabilizer off the tail.
The crash of the plane, in a farm field, killed all 17 aboard. It triggered the first substantial government backing for studies of swan migration routes by Dr. William J. L. Sladen, a Hopkins professor and world authority on these largest of the world's waterfowl.
By mid-March 1973, Sladen's team had wired a big swan for radio telemetry tracking. He was nicknamed Russell, for then-EPA Administrator Russell Train, at whose Talbot County farm the swan was captured.
Conditions were perfect for migration from the bay to Ontario, and a volunteer tracking crew was ready to scramble from Baltimore-Washington International Airport as soon as Russell departed. His liftoff came at 1 a.m. The plane was soon airborne, only to have Russell put down off Kent Island after an epic migratory flight of 18 minutes.
It was not the last frustration. Russell later slipped from the bay unnoticed by the electronic tracking system, and days later was found -- by accident -- resting peacefully on Lake Erie. He confirmed, however, a general pattern to the swans' northward flights: a premigratory restlessness, followed by a few short hops up the bay, or to places like Washington Boro; followed by setting off in earnest.
The first real success for the swan trackers came later in March, when their rented Cessna roared aloft around 10 p.m. one evening to follow a pair of swans from Blackwater National Wildlife Refuge in Dorchester County.
By 11 p.m., the plane caught up with the swans over Frederick. Swans and plane hopscotched that night and into the morning across Pennsylvania and Ohio.
The swans easily outflew the plane, which had to refuel, and the exhausted pilots had to catch a brief nap. Meanwhile, a ground crew kept tracking the swans; fortunately, the big birds took a course that followed the Ohio turnpike, more or less.
Around Toledo, the Cessna caught up again, and tracked the swans to a flooded field in Ontario, where they finally had landed for a brief rest.
A wealth of data flowed from that tracking flight and others ranging as far as Saskatchewan. Frequently, the swans used airspace populated by small aircraft -- 2,700 to 3,500 feet -- and averaged 30 mph or better on their own; when helped by tail winds, they hit 72 mph.
They were making the hop from Maryland to Ontario in 24 hours or less.
Later information would show that the return migration in the fall, aided by more frequent tail winds, was truly epic: The birds
on their final leg to the bay might fly nonstop for more than 1,300 miles, remaining airborne for up to 30 hours. Altitudes of three miles or more were observed.
Students of avian physiology say the same long, looping windpipe that creates the unforgettable music of the tundra swan also functions as part of a respiratory system that scavenges scarce oxygen at great heights with an efficiency not unlike that of advanced jet engines.
And aerodynamically, for all their bulk, swans in wind tunnel tests show less drag than eagles, ducks or geese. The shape that has appealed to poets and artists through the ages turns out to be also quite practical.
As for Russell, he turned up off the Train farm again in 1975, sans radio transmitter, having logged an estimated 10,500 miles since he was first banded on the bay.
To witness the staging of the swans and geese next year -- early to mid-March is the peak -- follow I-83 to York, Pa., and take Route 30 east toward Lancaster.
Cross the Susquehanna and turn right through Columbia, following the Conrail tracks downriver a few miles to Washington Boro. The birds usually fly out to feed in fields between dawn and 9 a.m.
A few miles farther down the River Road is the entrance (marked) to a rugged, two-mile trail that climbs Turkey Hill, one of the most spectacular overlooks of the Susquehanna.