Grassland Loss Threatens Duck Populations
The latest DU research underscores the importance of protecting remaining native prairie in the Dakotas
By Scott Stephens, Ph.D.
Nestled among the little blue-stem on a rocky ridge in the Missouri Coteau, a hen pintail patiently incubates her clutch of nine olive-colored eggs on a cool May morning. This region of the Dakotas is one of the few glaciated portions of the Prairie Pothole Region where large expanses of native grassland and high wetland densities remain intact. The hen hears a low hum in the distance, barely perceptible at first. As the humming grows louder, she becomes nervous.
Suddenly a hissing sound can be heard, and the surrounding grass is laid over. The pintail flushes from her nest. A loud “whoa” is hollered out, and the two ATVs dragging a chain across the prairie come to a stop.
The researchers on this Ducks Unlimited nest-searching crew quickly locate the pintail’s nest. They enter GPS coordinates of the nest’s location as well as the area’s habitat classification into their electronic database. Meanwhile, satellites collect data on the surrounding upland cover and other landscape characteristics. This pintail nest just became another small piece of information added to the database of more than 9,000 duck nests that DU has collected over the past six years.
DU’s goal in conducting this research is to refine its understanding of the factors that influence duck-nesting success on the coteau and other prairie landscapes vital to breeding waterfowl. DU uses this information to maximize the effectiveness and efficiency of its habitat conservation work in these crucial breeding areas. Analysis of the data collected over the past six years has yielded some important insights.
Most notably, DU’s evaluation and monitoring efforts have confirmed that of the many variables that influence duck-nesting success on the prairies, landscape-level habitat characteristics have the greatest impact. The three most important landscape characteristics are the amount of grassland within a 16-square-mile area, the amount of edge habitat between grassland and cropland within a four-square-mile area, and the density of wetland habitat within this four-square-mile area.
Ducks nesting on landscapes where large blocks of contiguous grassland remain intact have higher odds of hatching broods than ducks nesting in smaller tracts of grass on landscapes that have been fragmented by agriculture. The research also suggests that nesting success is lower on landscapes with a higher density of wetland habitat, perhaps because more wetlands attract more predators. In recent years, however, wetland density appears to have had a smaller effect on nesting success on DU study areas.
Environmental conditions can also have a significant influence on nesting success. Not surprisingly, the researchers have found that varying levels of precipitation on the prairies and accompanying changes in habitat conditions have a significant impact. Evidence is mounting that ducks often experience high nesting success—even in areas with low levels of grassland—during the first few years after water returns to the prairies following a prolonged period of drought. Drought conditions may depress populations of small mammals, insects, and other prey species. This in turn reduces predator populations that directly influence nesting success. When water returns to the prairies, breeding duck populations are able to quickly exploit new wetland habitats before predator numbers rebuild in these areas. Thus, environmental conditions may overwhelm landscape characteristics for a brief period of time.
Nevertheless, the preponderance of data reveals that landscapes with abundant grassland and low levels of fragmentation are much more likely to achieve the high nesting success required to grow duck populations. In fact, DU’s research suggests that areas with very high levels of intact grassland are four times more likely to achieve population-expanding nesting success than more fragmented sites. DU is currently using this information to target its conservation work in the most productive areas for breeding ducks. Unfortunately, recent trends in land use don’t bode well for grasslands or ducks.
In another part of the coteau region, another hen pintail sits patiently on eight eggs nestled in a clump of buffalo grass and blooming pasqueflowers. And another low hum can be heard in the distance. As the noise grows louder, this hen flushes from her nest just in time to avoid the blades of a plow churning up the grass around her. The prairie where the pintail was nesting had survived for thousands of years, but in a matter of hours the sod is tilled and seeded with new genetically modified soybeans. Sadly, this scene is repeating itself across thousands of acres of “old-growth” prairie each year in the Dakotas and eastern Montana.
Ducks Unlimited, in cooperation with The Nature Conservancy, the University of Montana, U.S. Fish and Wildlife Service, and South Dakota Department of Game, Fish, and Parks, has recently undertaken an important research project to examine native grassland loss rates across the Missouri Coteau of North Dakota and South Dakota. Since 1984, researchers estimate that nearly 144,000 acres, or 225 square miles, of native grassland have been lost in areas of the coteau where analysis was conducted. Presently, DU and its partners are using this information to develop models that will help target and protect the remaining tracts of native grassland at highest risk.
The science related to this problem is clear. Large tracts of native grassland are vitally important to maintaining healthy duck populations and many other grassland birds. But these strongholds of bird reproduction are being lost at alarming rates. In order to halt the loss of this crucial habitat, DU will need the support of everyone who shares an interest in conserving the prairie’s diverse flora and fauna, from pasqueflowers to pintails.
Dr. Scott Stephens is director of conservation planning at DU’s Great Plains office in Bismarck, North Dakota.