Nebraska’s Magical Spring Migration
Over the past fifty years I have often been asked why, of all the places I have lived and visited, I chose Nebraska as the place where I have decided to spend the rest of my life. I quite willingly admit that Nebraska lacks the mountain grandeur of Colorado, the wonderful rocky coastline of Oregon, and the stunning glaciers of Alaska. Yet I quickly point out that we Nebraskans can claim the continent’s largest remaining native prairie flora and its associated prairie wildlife, perched on the largest region of picturesque sand dunes in the western hemisphere. This in turn rests atop one of the greatest reservoirs of fresh water in the world, whose artesian springs give birth to such beautiful Sandhills streams as the Calamus, Loup, Dismal, and Elkhorn. Then, as a trump card, I say, “Oh yes, and for six weeks in spring we also have what is one of the largest and most spectacular concentrations of birds in the world.”
Compared with other spectacles I have seen, such as the great coastal seabird colonies of Alaska’s Pribilof Islands, Nebraska’s cranes and migratory waterfowl can be observed without fighting foul weather and high winds. The equally famous spectacle of at least a half million wildebeests migrating slowly across the Serengeti plains of Tanzania can be relatively boring and is also somewhat smelly. By comparison, there is boundless joy in sitting quietly among prairie grasses along the Platte River with an azure sky overhead and a chorus of crane music drifting down from a thousand feet above. As the silvery-gray birds wheel gracefully about in a giant vortex of life and call excitedly to one another as they descend to their safe and ancestral resting places in the river, I too know I have witnessed my personal Elysium.
There is a line in the movie Field of Dreams in which the ghost of the famous baseball player “Shoeless” Joe Jackson appears and, finding himself surrounded by a tall cornfield, says, “Is this heaven?” The response by the astonished landowner (Kevin Costner) was simply, “No, this is Iowa.” Every March, when I reach the vicinity of Grand Island while heading west from Lincoln on I-80, I too silently ask myself, “Is this heaven?” By then the sky becomes increasingly sprinkled with skeins of countless geese overhead, the fields of corn stubble are progressively covered with foraging sandhill cranes, and the crisp but gentle south wind is redolent with the promises of an oncoming spring. Between Grand Island and Kearney the Platte Valley is an ever-changing spectacle of cranes, geese, ducks, and other migrating birds, ranging from undulating flocks of red-winged blackbirds resembling giant apparitions as they drift gracefully above the land to lone raptors, such as rough-legged hawks and Harlan’s hawks, slowly working their way back toward their arctic breeding grounds.
Migrating waterfowl move into the Platte Valley from as early as mid-February in recent years, when the Platte River becomes ice-free and snowmelt in the nearby Rainwater Basin replenishes the shallow basins with enough water to provide resting and foraging sites for a dozen or more species of ducks and geese.
Even before the sandhill cranes have arrived in large numbers, ducks such as the common mergansers and common goldeneyes are likely to be seen forging along the ice-free opening of the river, and both mallards and northern pintails are likely to be seen coursing overhead in dizzying courtship flights. Soon they are supplemented by other dabbling ducks, including green-winged teals, American wigeons, gadwalls, northern shovelers, and diving ducks such as redheads, ring-necked ducks, lesser scaups, and canvasbacks. Among the last to arrive are blue-winged teals, finally back from widely scattered tropical wintering areas, and the tardy ruddy ducks, whose migrating males are usually still in their drab winter plumages.
There are few places in North America that, at least for a few weeks in March, support as much avian biomass as the central Platte Valley. Assume that each of the five hundred thousand sandhill cranes in the region weighs an average of six pounds and that snow geese are of similar weight. Between 2001 and 2003 there were estimations of from 1.2 million to 7.3 million snow geese, and a few thousand of the smaller Ross’s geese, in the Rainwater Basin and central Platte Valley, averaging 3.2 million for the three years. Add to this a million or more Canada, cackling, and greater white-fronted geese that average perhaps five pounds. There are also several million mallards and northern pintails averaging about three pounds, and unknown numbers of other ducks of varied weights, and the total avian biomass must easily exceed fifteen million pounds.
These numbers are far too large to comprehend, but the amount of food required to maintain the flocks is even more mind-boggling. Suffice it to say that, without the great quantities of unharvested grain left over in the nearby fields, such ornithological richness would be impossible. It was the great agriculture revolution following World War II, with new technology providing machinery, fertilizers, pesticides, and new irrigation techniques, that altered the historic Platte Valley of small farms and precipitation-dependent crops into an agricultural powerhouse. No wonder the cranes and geese found that the Platte Valley was the place to go to put on a maximum amount of fat in a minimum amount of time prior to migrating to high-latitude breeding grounds, where food is relatively scarce.
Nebraska provides North America’s most important spring staging grounds for both sandhill and whooping cranes, and the central Platte Valley contains the most important of all the state’s wetlands for both species. For the sandhill cranes, it is the combination of the Platte River as an ideal roosting habitat and the nearby cornfields as a convenient source of easily gathered food. For the whooping cranes, the Platte is less attractive as a roosting habitat than it was historically, since so much of it has been overgrown with shoreline and island vegetation. The foraging niche of whooping cranes is more water-based than is the sandhills’, with much of the whooping crane’s traditional foods obtained from shallow ponds, marshes, or estuaries. Nevertheless, these endangered cranes still annually stop in the Platte Valley. They sometimes feed in cornfields along with sandhill cranes, but they are more often found in rather remote wetlands and riparian lowlands both south and north of the immediate Platte Valley.
We have no idea as to how long this magnificent spectacle has gone on. Cranes have waded the wetlands of the world for at least fifty million years, a period more than ten times longer than the time since ancestral humans first walked upright. They have probably migrated across what is now Nebraska for several million years, or longer than the Platte River has been in existence. It seems likely that, at the end of the Pleistocene epoch more than ten thousand years ago, as outwashes from the retreating glaciers of the northern plains were spilling into the Missouri River and the glaciers of the western mountains were also melting, the Platte River or its antecedents had their origin, carving new water routes through the tundra-like landscapes of the central plains. We can also imagine that sandhill cranes and other arctic-adapted birds such as snow geese annually followed the warming landscape northward, breeding during the brief summers and retreating to ice-free wetlands each winter.
No doubt early Native Americans saw and rejoiced in these flights; they must have represented a vital source of fresh meat after a winter of probable near-starvation. But the crane migration remained largely unknown until very recent times; early immigrants following the Platte west typically didn’t cross Nebraska Territory until late spring, so that they might cross the mountain passes of Wyoming during the snow-free period of summer.
The first estimates of the crane migration date from the early 1940s. A writer in the April 19, 1934, Hastings Daily Tribune hypothesized that the stretch of the Platte between Kearney and Odessa “is crossed twice a year by more sandhill cranes than any other strip of similar length in the same latitude anywhere from coast to coast.” In 1945 Dr. William Breckenridge, an ornithologist from the University of Minnesota, provided one of the first numerical estimates of spring crane numbers in the central Platte Valley. His counts suggest that in this period, before the advent of extensive use of fertilizers, pesticides, and irrigation, the numbers of sandhill cranes seen near the confluence of the North Platte and South Platte Rivers were in the general range of thirty thousand to forty thousand birds. No contemporary estimates of birds farther downstream are available, but one might imagine a regional population of no more than one hundred thousand or so birds existed then.
By the early 1960s, with the legalization of sandhill crane hunting in Texas and New Mexico, the U.S. Fish and Wildlife Service began systematic surveys of spring sandhill crane numbers in the Plate Valley, where essentially all of the midcontinent arctic-breeding lesser sandhills and many of the subarctic-breeding “Canadian” sandhill cranes concentrate in March. Early survey estimates were subject to great variation but generally ranged from about 150,000–200,000 cranes. By the mid-1970s U.S. Fish and Wildlife Service data suggested a maximum Platte Valley population of 200,000–270,000 sandhills. Since then the population estimates for the Platte Valley have gradually crept upward, so that now 450,000–500,000 represents the generally accepted estimate. This estimate has remained fairly stable recently and has been generally supported by independent ground surveys and other methods of aerial survey.
It is difficult to know what factors might have prompted the remarkable growth of the midcontinent population of sandhill cranes during the past seventy years, but the massive increase in corn production in the Platte Valley since the 1940s and the attendant availability of unharvested corn left in the fields each fall has certainly been important. This corn bonanza has provided a nearly unlimited source of food for cranes as they move north in the spring, when they need maximum fat storage to prepare them for the rigors of their remaining migration and the stresses associated with an arctic nesting environment. Quite possibly the amelioration of the climate in arctic regions has also had an important effect. By lengthening the frost-free period to a point that the nearly one hundred days required for nest building, egg laying, incubation, and chick rearing can now often be comfortably fit between the last spring blizzard and the first fall snows.
Even with a successful breeding season a pair of sandhill cranes only infrequently manages to produce and raise two chicks from their two-egg clutch to fledging. Besides other losses, one of the eggs (the first laid) always hatches a day or two before the other, and the first-hatched chick may fight with and might even kill its younger sibling. Should both young fledge, however, the family soon forms a strong social bond, which is held together by mutual calling and postural displays. A juvenile crane is likely to remain closely attached to its parents for up to about three years, when sexual maturity leads to independence. Many of the sandhill cranes breeding in the mild climate of Florida may attempt to breed when only two years (in males) to three years (in females) of age. However, it is believed that arctic-breeding cranes undergoing the stresses of long migrations and extreme climatic conditions may require up to five years in order to achieve breeding status.
How long social attachments among parents, siblings, and other close relatives persist is still uncertain in wild cranes. It is generally true that all species of cranes form permanent pair bonds, but these are often broken by the death of one of the partners or, less often, by divorce. Divorce is rare among sandhill pairs that have a history of successful reproduction, and the ability of the male to establish and maintain a desirable nesting territory seems to be a major factor in determining whether a pair bond will be maintained between seasons.
Family bonds among whooping cranes may be stronger than those in sandhills. Long-term observations of color-banded birds has shown that the small flock sizes typical of whooping cranes result from the long-term social attachments of closely related individuals, so that as many as four generations of birds can be present in a single migrating assemblage. This factor, along with the great potential longevity of cranes, often exceeding thirty years in protected populations, allows for real cultural transmission of information from generation to generation. The older birds may actively or passively pass on important information about migration routes and migratory staging areas as well as suitable and secure breeding and wintering sites.
Through such intergenerational learning, it is likely that an adult arctic-breeding sandhill crane knows more about the intimate geography of North America than does a professional airline pilot. Furthermore, each arctic-breeding crane must undertake these hazardous migrations of three thousand to four thousand miles or more twice yearly. These migrations are performed in the face of legal hunting in every Canadian province and almost every American state located on the birds’ migration route between Alaska or Canada and Texas. Nebraska is the only Central Flyway state that has never attempted to obtain permission from federal authorities for initiating a sandhill crane hunting season.
Sandhill crane killing for “sport” has greatly increased in popularity since its initiation in Texas and New Mexico in the early 1960s; now roughly forty thousand cranes in the midcontinent population are killed each year, which is about 8 percent of the total, or most of each year’s total production of juveniles. This annual hunting mortality rate means that a crane living in the Central Flyway has about a 50 percent greater danger of being killed during any single year at the hands of a hunter than did a U.S. soldier serving over the entire ten-year period of the Iraq War.
For those sandhill cranes that survive the long hunting season and winter months in the playa wetlands and marshes of Texas, New Mexico, Arizona, and Mexico, their safe return to the Platte River and its surrounding corn-rich valley can only be a vast relief. We humans too can also briefly forget our worries of daily life by visiting the Platte Valley in early spring and getting a glimpse of wild America. One need not be a bird expert to enjoy this almost incredible visual and auditory experience, which I can promise will indelibly last for a lifetime.
Visitors to the central Platte Valley may choose to experience a sunrise or sunset roosting flight in a commercial blind, such as at Audubon’s Rowe Sanctuary near Gibbon, or one operated by the Crane Trust’s Nature and Visitor Center at the I-80 Alda interchange near Grand Island. Or one may simply watch the amazing passing parade of cranes, geese, and other birds from one of the two public viewing platforms, which are located at the Platte River bridges along the highways directly south of Alda and Gibbon. In any case, don’t pass up a sunrise or sunset experience in favor of a quick trip; to do so is to cheat yourself out of a brief glimpse of nirvana.