Nesting Ducks Get a Helping Hand from Delta Waterfowl
Posted on 11/22/2002
BISMARCK, ND—With much of the northern breeding grounds in the grasp of a severe drought, waterfowl biologists were less than optimistic about the prospects for duck production this spring. History told them a high percentage of ducks wouldn’t even attempt to nest, and those that tried would face an uphill struggle for success.
But if production across most of the prairie pothole region was sub-par, nest success (the percentage of nests that hatch at least one egg) soared to population-expanding levels at five key locations in North Dakota. Those sites—which occupied close to 100,000 total acres—were enrolled in Delta Waterfowl’s ongoing predator-management program.
Delta began its predator research in 1994 in an attempt to determine whether protecting nesting ducks from unnaturally high populations of predators would improve nest success. Trappers were hired to reduce the numbers of mammalian predators—mostly raccoons, skunks and foxes—on experimental study sites. Nest success on these managed sites was compared to similar areas of breeding habitat that were not trapped (un-managed sites).
In 2002, Delta expanded its efforts to include four 36 square mile management sites (total of 92,160 acres) and ten 1 square mile (6,400 acres) experimental blocks. Delta Scientific Director Serge Lariviere was encouraged by the results. “With the tough conditions ducks faced on the breeding grounds this spring, we are happy to see the strong nest success on our managed sites,” Lariviere said. “If it hadn’t been for predator management, we feel strongly that nest success and production from those sites would have been much lower. The results from Egeland support that belief.”
At the Egeland experimental site, nest success on ten 640-acre predator blocks averaged 42 percent while nest success on ten similar-sized control blocks (not trapped) averaged 20.6 percent.
Of the four 36 square mile sites the most productive was Cando in northeastern North Dakota’s drift prairie, where 40.3 percent of the 1,374 nests sampled by Delta student researchers were successful. Mallards were the most abundant species with 578 nests. Last spring marked the fourth straight year Delta has managed predators on the Cando site in conjunction with the USFWS’ Devils Lake Wetland Management District.
The remaining predator management sites were at Stanley, ND (35.6 percent nest success), Arrowwood Wetland Management District (35.2 percent) and Pleasant Lake, ND (22.5 percent).
“Since we started our predator work, our data have shown that managing predators increases nest success 2 to 3 times,” says Lariviere, “and this year was no exception. Given conditions on the prairies, we’re quite happy with the 2002 results.”
Across the prairie breeding grounds nest success has dropped steadily since 1935 when it was documented at 33 percent. By 1955 nest success had dropped to 21 percent, in 1970 it stood at 15 percent and by 1992 nest success was just 10 percent. Countless studies have shown that nest and hen predators are the primary cause of declining production.
Prairie ducks did not evolve with the current mix and density of predators. Raccoons, skunks and foxes existed in very limited number—if at all—across the pothole region prior to European settlement. The eradication of the gray wolf early in the century and a the establishment of new denning sites such as abandoned barns and farm houses and the abundance of food provide through agriculture and ranching allowed fox, raccoon and skunk—predators that exist in far greater densities than wolves or coyotes—to expand their range.
Scientists say 15 to 20 percent nest success—the exact figure varies from species to species—is necessary to maintain the existing populations. Anything below that level results in what scientists call a population sink, which means ducks nesting in that area do not produce enough young to replace annual losses.
During the first three years of Delta’s experimental predator work (1994-1996) under Delta student researcher Pam Garretson, ducks on un-managed sites averaged 16 percent nest success while ducks on similar sites where predators were managed averaged a whopping 46 percent. Garretson sampled 16-square-mile blocks in North Dakota.
In 1997 and 1998, Delta student Mike Hoff compared nest success on 36-square-mile tracts and found 15 percent nest success on un-managed and 36 percent on predator management blocks. Predator management holds great promise to significantly increase duck production in many key areas of the Prairie Pothole Region as demonstrated by Vance Lester’s predator management work in Saskatchewan. Lester’s work on 16-square-mile tracts between 1999 and 2001 produced 48 percent nest success on managed sites vs. 19 percent on un-managed sites.
Scientists know that large blocks of dense nesting cover may provide a buffer against predators. Recent research has shown that ducks often achieve population-expanding production rates in areas where 40 percent or more of a township has grassy upland nesting cover, provided suitable key moisture exists. Such areas exist in the western portions of the Dakota and eastern Montana, where ranching is the dominant agricultural activity. Across the eastern portions of the region—where farming is more prevalent—nesting cover is severely reduced, making it easier for predators to find and destroy nests and hens.
However, these intensely farmed areas continue to attract significant numbers of nesting ducks. Delta has focused its predator management on areas where nesting activity is high but nest success is low.
Last spring—in an effort to identify the most productive sites for predator management—Delta enlisted the services of Fish and Wildlife’s Habitat and Population Evaluation Team (HAPET). Ron Reynolds and Chuck Loesch produced a model that was used to develop a Geographic Information Systems-generated Predator Management Decision Matrix. By using GIS, Delta will be able to focus its predator work on sites with the highest breeding duck-pair densities and fragmented nesting cover which commonly results in overall poor production. “This effort will allow us to target new predator management sites using the best available information,” states Lariviere. “This will ensure that as the program grows and we continue to add sites, that we are investing duck hunter’s dollars to increase duck production in the most efficient manner.”
Lariviere concludes, “Six decades of waterfowl research indicates that poor duck production is the norm across vast majority of the breeding grounds. Delta’s predator management research shows what managers can do to produce ducks, on habitats where duck production is an important objective.”
Delta Waterfowl was established in 1911 and is North America’s leader in waterfowl conservation research. Delta’s U.S office is in the heart of duck country, Bismarck, North Dakota. Delta’s mission is to enhance waterfowl populations while securing the future of waterfowling.