The tallgrass prairie of North America is a unique environment, harsh and delicately balanced by turns, and in Seasons of the Tallgrass Prairie (University of Nebraska Press, 2014) Paul A. Johnsgard celebrates the astonishing beauty of the Great Plains. From reflections following a visit to a Pawnee sacred site to meditations on the perils facing the state’s finite natural resources, these essays are the result of a lifetime spent roaming Nebraska’s back roads, trails and sometimes-forgotten places. The following excerpt is from chapter 9, “The Whooping Cranes Are Still Surviving Tough Odds.”
Although many Nebraskans have had the indescribable pleasure of watching tens of thousands of sandhill cranes overhead, or even seeing them roosting on Platte River bars and islands during spring migration, only a tiny handful can say that they have ever seen whooping cranes in Nebraska. The sheer odds against it are daunting. Compared with 450,000–500,000 sandhill cranes migrating through the state each March, there are now less than 300 whooping cranes in the flock that annually migrates from Aransas National Wildlife Refuge, on Texas’s Gulf Coast, to Wood Buffalo National Park, straddling the border of Alberta and Canada’s Northwest Territories. In addition to this numerical population disparity, whooping cranes migrate somewhat later in spring than the sandhills (during April in Nebraska), after most crane-watchers have gone home. During daytime foraging they also usually frequent rather remote wetlands far from any roads, and they generally move in small groups—a pair or a family or extended family that often consists of a pair and one or more generations of their offspring.
I have spent over fifty years studying, thinking, and writing about cranes and have observed cranes from Alaska to Arizona annually since 1961. My younger colleague, Dr. Karine Gil-Weir, engaged in full-time research on crane longevity, familial relationships, and migratory traditions in Texas and Nebraska from 2002 to 2011. Our devotion to these birds might be considered obsessive-compulsive behavior by many, but the sights and sounds of wild cranes are as intoxicating to us as the odors of tropical wildflowers. To be able to experience them only once would be as painful as being condemned to observe only a single sunset during one’s lifetime.
A lifelong attraction to cranes among many people means that we now know as much about the lives of sandhill and whooping cranes as we do about almost any other North American bird. In 1941 only twenty-two whooping cranes existed in the wild (sixteen in Texas and six in coastal Louisiana). The Louisiana population was extirpated in 1949. It was not until 1954 that their Canadian breeding grounds were discovered (serendipitously, they are located in a remote subarctic area that had already been preserved, as Wood Buffalo National Park), and it was not until 1986 that the world population reached one hundred individuals. The whooping crane was listed as a nationally endangered species in 1972, which made available federal funding for research and for developing a survival strategy, although a wildlife refuge (Aransas National Wildlife Refuge) had been established to protect their wintering grounds almost a half century previously.
Tracking Whooping Crane Migration Patterns
It is an ironic fact that the whooping crane’s perilous population status has protected the Platte River from destruction by powerful irrigation interests, through the identification of the central Platte Valley as a critical habitat for the species. The threat of the extinction of the whooping crane, along with three other threatened or endangered birds and fish, has helped preserve Platte habitats for many other water-dependent species and set the stage for the enactment of a massive Platte conservation effort in 2006. This plan approved a multimillion-dollar, thirteen-year Platte River Recovery Implementation Program for wetland preservation and restoration in Nebraska, involving the federal government and the three states located in the Platte River drainage.
The central Platte Valley was the first region between Texas and the Canadian border to be federally designated as critical habitat for migrating whooping cranes. Other Great Plains sites that have since been similarly identified as critical habitats include Oklahoma’s Salt Plains National Wildlife Refuge and Cheyenne Bottoms State Wildlife Area and Quivira National Wildlife Refuge, both in Kansas.
Among more than five hundred spring observations of whooping cranes obtained between 1943 and 1999 and analyzed by Jane Austin and Amy Richert, the largest percentage (69 percent) were from Nebraska locations, proving the critical importance of the Platte and other Nebraska rivers to migrating whooping cranes. There were progressively fewer migratory sightings in North Dakota, Kansas, South Dakota, Montana, Oklahoma, and Texas. Among nearly five hundred fall migration records, the largest share (33 percent) was also from Nebraska, followed sequentially by Kansas, North Dakota, Oklahoma, South Dakota, Montana, and Texas. In Nebraska most historic sightings of migrating whooping cranes have occurred along the central Platte River, but they also have included the Niobrara, Middle Loup and North Loup rivers. In 2010 the most frequently visited counties during spring were Custer (nineteen records), Kearney (eight records), and Buffalo (eight records). Austin and Richert found that most locations where cranes have been observed were over a half mile from any human structures or developments. Most were more than a third of a mile from the nearest power lines, and about half of all the roost sites and two-thirds of the foraging sites had unobstructed visibility for more than a quarter mile and were associated with river widths greater than seven hundred feet. Clearly, visibility and distance from human activity are important aspects of whooping crane requirements. They also need access to wetlands for both foraging and nocturnal roosting. Like sandhill cranes, they prefer to roost in shallow water, well away from heavy shoreline or island vegetation.
Austin and Richert also determined that the average date for spring migration sightings is April 6 in Oklahoma, April 12 in Kansas and Nebraska, April 19 in South and North Dakota, and April 26 in Montana. In Nebraska, records that I have summarized similarly indicate that the peak spring migration period is the two-week-period of April 1–15 and the peak of fall migration is October 11–24. Starting in 1979, individual whooping cranes have been arriving in Nebraska much earlier than previously had been the case, probably because they had become socially attached to sandhill flocks that now typically arrive in mid-February rather than early March.
Partly in order to better document the role of individual cranes in migration and their population structure, a program of color-banding juveniles was undertaken in 1977 (when there were only sixty-two adults and thirteen juveniles at Wood Buffalo Park) and was continued until 1988. Gil-Weir has analyzed the survival and individual reproductive success from these banding efforts. Based on subsequent observations on the breeding grounds, on migration, and at Aransas, she determined that 24 of the 132 banded birds were still surviving as of 2009. All the survivors were at least twenty-two years old, and one had reached thirty-two years of age. Many cranes of various species are known to have survived more than thirty years in captivity (but rarely more than seventy), and some wild sandhills are also known to have had attained similar life spans.
Although first-year survival of banded birds averages 42 percent in Gil-Weir’s analysis, survivorship of subadults increases annually until they reach four years of age. Older age-classes of whooping cranes have the highest mean survival rates and breeding success, reaching a maximum fecundity at about fourteen years of age. Indeed, one female at Wood Buffalo Park was still nesting at twenty-seven years of age.
Because whooping cranes are federally protected, various accidents are probably the major cause of adult mortality, especially collisions with overhead utility lines by migrating birds. By comparison, sport hunting is the cause of most mortality in sandhill cranes, resulting in the death of more than 5 percent of the lesser sandhill crane population annually. Thankfully, hunting for sandhill cranes in Nebraska has never been allowed, because of the special importance of the Platte to whooping cranes.
Partly because of their great longevity, and their strong family bonds, it is of interest to track individual and population characteristics among color-banded birds. Gil-Weir has determined such times of initial breeding, breeding success, length of pair bonds, incidence of remating after loss of a mate, and many interesting intergenerational associations. These include such information as the distances between the nests and wintering territories of parents and offspring and the common use of migratory stopover areas by close relatives, through four generations. Of special interest is the genetic legacy of a single identified pair that produced four descendants; from three of them that were banded it was possible to estimate that at least forty-three direct descendants contributed to the wintering Aransas population from 1977 to 2007. During that period the pair produced at least eighteen second-generation offspring that survived long enough to reach the Texas wintering grounds. The same genetic line subsequently produced seventeen third-generation birds and four fourth-generation offspring that likewise were able to survive the two-thousand-mile flight to Texas. Remarkably, many of these birds have continued to use the very same migratory stopover points as did their great-grandparents, showing the power of place memory in crane migration and the probable importance of migratory traditions in long-lived and long-distance migrants such as cranes.
Whooping Cranes in the Future
The Aransas–Wood Buffalo flock has recently undergone some hard times, especially during the winter of 2008–09, when a severe drought in Texas resulted in the loss of 23 of its early winter population of 270 birds, a result of excessive freshwater withdrawals from the Guadeloupe and San Antonio Rivers by the local river authority that raised the estuary’s salinity and killed much of the cranes’ invertebrate food base, especially blue crabs. A year later, the total 2009–10 winter population at Aransas was about 263. With the retirement of Tom Stehn, the refuge’s whooping crane expert, who had carefully counted every last wintering crane annually for twenty-nine years, the protocol for counting the wintering birds changed, using incomplete sampling and extrapolated population estimates. The new survey method was first used for the 2011–12 flock, which produced an estimate of 254 birds in or near the Aransas refuge but had a margin of statistical error of 62 birds. A more recent, 2012–13, estimate, of 273 birds (statistical range 178–362), suggests that the Aransas–Wood Buffalo crane population is simply holding its own. The overall world population of whooping cranes in early 2013 was about 600 birds, of which 445 existed in the wild, with the rest in confinement for breeding and research.
In the spring of 2010 nine chicks were banded and tagged with satellite and VHF radio-telemetry transmitters by the Crane Trust, the Canadian Wildlife Service, and other collaborators. This was the start of a four-year program that, from 2010 through the 2012 nesting season at Wood Buffalo Park, captured and tagged a total of thirty-one chicks out of a proposed total of forty. Since there had been a hiatus of more than twenty years since banding was last done on the breeding grounds, it is hoped that these current bandings will result in new sources of valuable population data for the understanding and conservation of this endangered species throughout its migratory corridor.
For the biologists who have worked so hard to restore whooping cranes, even small miracles such as the gaining of a few chicks per year must be rewarding. At times like these, with oil pollution in our precious Gulf Coast leading to the sight of majestic seabirds such as brown pelicans dripping with oil, the thought of immaculate whooping cranes flying high overhead is comforting, offering a reminder that we must all act to keep natural treasures such as cranes a reality.
Excerpted from Seasons of the Tallgrass Prairie: A Nebraska Year by Paul A. Johnsgard by permission of the University of Nebraska Press. © 2014 Board of Regents of the University of Nebraska. Available wherever books are sold or from the University of Nebraska Press 800-848-6224 and at nebraskapress.unl.edu.