The Science and Strategy of Habitat Conservation in the Rainwater Basin

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By Doreen Pfost

When wild birds fill the skies above south-central Nebraska each spring, their voices seem to echo across the past and carry the memory of countless, massive migrations that once characterized the Great Plains.

What might northbound birds have seen from above as they flew into this region? To migrating ducks, geese and cranes, the Rainwater Basin must have looked like a watery paradise: From western horizon to east, thousands of wetlands, large and small, glittered in a vast prairie. Ahead, in the distance, was the long curve of the Platte River, flowing toward the sunrise.

For millennia Rainwater Basin wetlands provided a secure roost to migrating birds, and beneath the shallow water lay a bounty of energy-rich food. Later in the spring, after the ducks and geese had flown north, migrating shorebirds feasted in the declining water and on surrounding mudflats.

Northern pintails fly across the recently restored wetland at Hansen Waterfowl Production Area in March 2013. (Doreen Pfost)

Today the birds’ view is starkly different. Water pools in just a fraction of the Rainwater Basin wetlands that once existed, and the wetlands that remain are surrounded by nearly three million acres of highly productive farmland, crisscrossed by a grid of dirt roads and highways and punctuated by dozens of cities and towns.

Despite these changes, the Rainwater Basin is still the linchpin of the Central Flyway migration route. Millions of migrating waterfowl and shorebirds, traveling from their wintering grounds to their northern breeding grounds, stop here to rest and to eat. And eat.

They eat because they must accumulate sufficient energy reserves, in the form of body fat, to not only see them through migration but to improve the likelihood that they will successfully nest and add a healthy brood of offspring to their population.

Since 1992, the Rainwater Basin Joint Venture (RWBJV) partnership has worked to ensure that this region can meet the physiological needs of migrating birds. The RWBJV is one of twenty-two Joint Venture partnerships whose mission is to conserve bird habitats in regions across North America.

Like most Joint Ventures, the RWBJV was created to help achieve the goals of the 1986 North American Waterfowl Management Plan (NAWMP) by providing sufficient wetland habitat for ducks and geese. The RWBJV now contributes to conservation planning for a wide variety of birds throughout Nebraska’s mixed-grass prairie region; still, the wetlands of the Rainwater Basin remain the partnership’s primary focus.

But what constitutes “sufficient” wetland habitat? Certainly the Rainwater Basin landscape will never again contain the number of wetlands it once did. Approximately 99 percent of the region’s land is privately owned, and nearly three-quarters of the land is farmed—including many of the acres that previously held wetlands. The number of acres that could potentially be purchased or restored for wildlife habitat is therefore extremely limited.

Likewise, the funding, personnel, and other resources needed for conservation are limited and have come under increasing pressure in recent years. RWBJV partners recognized, therefore, that they must identify the opportunities for purchase and restoration that would provide the greatest habitat benefit per dollar invested, and they must ensure that every acre of already-protected land is managed to provide more and better habitat.

The RWBJV’s 1992 Implementation Plan aimed to achieve the approximate quantities of wetland and native grassland acres that had existed here in the 1970s. For two decades Joint Venture partners worked toward those goals. By 2013 the US Fish and Wildlife Service (USFWS) Rainwater Basin Wetland Management District managed fifty-nine Waterfowl Production Areas (WPAs) in the Rainwater Basin region, and the Nebraska Game and Parks Commission (NGPC) had thirty-five Wildlife Management Areas (WMAs). Over five thousand acres were in the Natural Resources Conservation Service’s Wetlands Reserve Program (WRP), and additional wetland acres had been protected by Ducks Unlimited and by conservation easements. Until recently, however, conservation partners lacked the tools to judge whether the growing number of habitat acres would be sufficient.

Late last year the Joint Venture finalized and adopted a revised Implementation Plan that takes a different approach, relying on Geographic Information Systems (GIS), aerial photography, and decision support tools developed by the RWBJV Science Office. As a foundation for other habitat information, the Science Office first developed the Annual Habitat Survey, a method to identify the average quantity and quality of wetland habitat available in the 160-mile-wide Rainwater Basin region during spring migration. Since 2004, the RWBJV has contracted with a specialized aviation company to fly over the region in mid- to late-February to take color infrared aerial photographs. Using GIS and Remote Sensing software, technicians mapped the locations and sizes of wetlands, plus wetland plant communities and areas of “ponded,” or standing, water. (The presence of water is crucial because wetland forage must be submerged in order for ducks to feed on it.)

The resulting maps made it possible to evaluate and compare the water and the plant communities on publicly owned wetlands, privately owned wetlands with conservation easements, wetlands enrolled in WRP, and private wetlands in short-term conservation programs.

The Rainwater Basin is a 6,100-square-mile wetland complex that includes all or part of twenty-one counties in south-central Nebraska.   Source: Rainwater Basin Joint Venture

The Science Office also developed a GIS-driven model that identifies and assigns relative weights to characteristics of the wetlands that waterfowl seem to prefer. A similar model was developed for whooping cranes, which regularly make migration stops in western Rainwater Basin wetlands. This information can be used to “score” and then prioritize sites that are candidates for protection, restoration, or enhancement.

The new Implementation Plan is based on estimates of the amount of food energy—measured in kilocalories—that meets the daily energy needs of migrating ducks and also adds body fat. RWBJV Coordinator Andy Bishop and NGPC Waterfowl Program Manager Mark Vrtiska consulted fellow biologists and research publications to make estimates and determine the approximate number of kilocalories available from an acre of seed-producing wetland plants.

The total quantity of kilocalories required region-wide will depend on the number of ducks that stop over and the number of days that each bird stays. RWBJV partners’ wildlife biologists estimate that if NAWMP goals are achieved in the Central Flyway, about 4 million mallards will migrate through this region each spring, along with 1.4 million northern pintails, over 800,000 blue-winged teal, and hundreds of thousands of ducks of other species, for a total of approximately 7 million ducks.

Many ducks feed on waste corn in farm fields, which provides significant food energy, but for other nutrients, research indicates that ducks require the foods found in wetlands.

In addition to ducks, white-fronted geese and Canada geese at NAWMP-goal levels would number over 750,000. Lesser snow geese and Ross’s geese appear to have exceeded NAWMP population goals and have grown beyond wildlife biologists’ current ability to accurately survey or count.

On the other hand, geese feed principally on waste corn while in the Rainwater Basin, so their numbers have a relatively small impact on estimates of wetland food sources.

The RWBJV biologists again turned to prior research to estimate the percentage of each duck species’ diet that should ideally come from wetland food sources, based on observation of the species’ feeding habits in this and other regions. This final estimate allowed them to calculate that the Rainwater Basin must produce sufficient communities of seed-producing wetland plants to provide approximately 4.4 billion kilocalories of food energy for migrating ducks and geese. This number can, in turn, be translated into the number of wetland acres that would be sufficient if water and plant communities were optimally managed. Science shop estimates suggest that adding about eight thousand acres of publicly owned wetlands, nine thousand acres of wetlands with conservation easements, and five thousand acres in short-term conservation programs would achieve the partnership’s goals.

Bishop notes that the RWBJV used energetics models and planning methods developed by other Joint Ventures in regions where birds overwinter. “We were able to build on planning techniques that have been used for decades in the Lower Mississippi Valley and the Central Valley. We just twisted the models a bit to apply them to migration habitat, which I sometimes call, ‘the last bastion of waterfowl ecology.’”

Vrtiska notes an added benefit of adapting models used by other Joint Ventures: “It gives us a common currency in talking with each other, which helps because we’re all trying to put habitat on the ground to reach a common objective.”

Energetics models do not address every aspect of habitat needs: They exclude, for example, the need for larger areas, relatively free of disturbances, where birds may loaf. But they provide a standard approach that partners across the country can easily grasp when engaged in cooperative efforts.

It’s one thing to calculate a need for 4.4 billion kilocalories of wetland seeds; it’s another matter to help generate that level of seed production. To achieve that goal, the RWBJV partners try to combine sound science and smart strategy.

For example, Ronnie Sanchez, project leader for USFWS’s Rainwater Basin Wetland Management District, notes the strategic value of purchasing “roundout” parcels: privately owned wetland acres adjacent to an existing WPA or WMA, the purchase of which would bring the entire wetland footprint into undivided, public ownership.

“That allows a many-fold increase in our ability to efficiently manage the habitat,” he says. With complete ownership of the wetland, water levels can be manipulated, prescribed burns and grazing programs can be more easily implemented. But agencies can only buy land if it’s for sale. “We don’t work in a vacuum,” says Sanchez. “We have to work with willing landowners and recognize that they have their own priorities.”

Apart from roundout acquisitions, many public lands—and wetlands in long-term conservation programs—benefit from another GIS tool developed by the Science Office, which identifies opportunities to restore the hydrology of wetlands and their watersheds.

Most public Rainwater Basin wetlands have been impaired to some degree by “reuse pits”: excavations that collect and store water for gravity irrigation systems. The pits are often on private farmland outside the WPA or WMA, but they capture water that would otherwise flow to the wetland. A growing number of reuse pits are being rendered obsolete as landowners change to pivot irrigation systems, but the expense of earthwork to fill the pits far exceeds the benefit gained from an additional acre or two of farm ground.

The Science Office’s mapping project identified reuse pits that, if filled, would most significantly improve high-priority wetlands. The wide array of partners that have contributed to this effort is an indication of the value of pit removal, or “hydrologic restoration,” in bringing back a wetland’s function. Funding has come from the Nebraska Environmental Trust; the NRCS; the USFWS Partners for Fish and Wildlife program; USFWS Cooperative Recovery Initiative grants; NGPC; and Ducks Unlimited, through a North American Wetlands Conservation Act grant.

Most recently, a team of biologists from partner organizations collaborated to develop a manual of “Best Management Practices” for Rainwater Basin wetlands. The document is designed to help wetland managers predict the results of various management practices—such as grazing, prescribed fire, herbicide, or disking—in suppressing growth of invasive plants and encouraging seed-producing wetland plants. Bishop says, “The Best Management Practices document helps land managers learn from each other and allows them to consider the cost-benefit of management practices, so they can make strategic decisions in allocating resources to improve habitat.”

Achieving the best possible habitat despite limited resources is the goal of all of the RWBJV partners. Although humans have put this landscape to work, it can still work for wildlife, too. As long as there is sufficient habitat, those of us who stand on the ground looking up can continue to experience the wonder of one of the world’s great migrations.

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