Spring surveys show resilience in North America's waterfowl. Yet come fall, hunters don"t always see the numbers they expect.
By Jason Abraham
In two days John Solberg will be in his element—flying a Cessna 185 single-engine airplane low and slow over prairie wetlands in the eastern Dakotas, counting ducks and geese as they pair off to bring a new generation of waterfowl into the world. But on this last Friday of April, he's in his office in Bismarck, N.D., sorting through papers, testing laptop computers, and assembling a small collection of fire-retardant flight suits.
The U.S. Fish and Wildlife Service pilot-biologist is preparing for the coming three weeks, in which he'll fly about 5,000 of the 54,000 miles covered by the North American May Waterfowl Breeding Population and Habitat Survey—believed to be the most extensive and comprehensive long-term annual wildlife survey in the world.
For each of the past 50 years, the endeavor to estimate North America's breeding waterfowl population has played out in the skies above waterfowl breeding grounds in Canada and the northern United States. During the survey, USFWS pilot-biologists visit 2 million square miles of isolated prairie ponds, flying about 150 feet above the ground and counting waterfowl. Last year's breeding waterfowl population estimate for the traditional survey area, which includes portions of Canada, Montana, and the Dakotas, was about 32 million birds. That's down from the 50-year average of 33 million.
The count begins in early May. Pilot-biologists usually finish their routes by early June. State biologists in Minnesota, Michigan, and Wisconsin also conduct aerial surveys about the same time. The USFWS Division of Migratory Bird Management compiles all of the data from federal and state biologists into an annual report.
Federal biologists use the aerial survey data to create the framework within which state agencies may select their waterfowl season length and bag limits. When waterfowl populations are low due to poor wetland conditions, wildlife managers shorten seasons and reduce bag limits to reduce harvest.
"The breeding waterfowl data set is the envy of biologists all over the world," Solberg says. "It's very rewarding to know the numbers generated from our data will help perpetuate migratory waterfowl."
During the past five decades, the aerial survey data have shown the resiliency of North American waterfowl populations, says Ray Norrgard, wetland wildlife program consultant for the Department of Natural Resources.
"When the prairies are dry, the numbers dip," he says. "But when there's rain and grass, the ducks come back.
"The good news is that since the mid-1990s, we've had good rainfall and adequate habitat due to land protection through federal and state agencies, as well as the Conservation Reserve Program," Norrgard says. "The bad news is that we could have absolutely incredible duck numbers if we"d had better habitat."
In 2005 Minnesota's breeding duck survey estimated 632,000 ducks, excluding scaup. Though roughly equal to the long-term average of 630,000, the abundance of ducks decreased 34 percent from 2004 and 10 percent from the 10-year average. The 2004 survey tallied about 1 million ducks, yet hunters last year suffered through one of the worst duck seasons in history. As many duck hunters found out, the number of breeding ducks doesn't necessarily correspond to hunters" success everywhere.
Although the statewide duck harvest continues to rank among the top 10 nationally, hunters in western Minnesota say they're not seeing the duck numbers they once did. Researchers say the spring survey can't predict hunting success locally. Fall weather and local habitat conditions determine where and when hunters bag ducks and geese, says Ken Gamble, Mississippi Flyway representative for the USFWS.
"It's kind of a game of expectations," he says. "Hunters see a high number of breeding ducks in the survey, long seasons, and liberal bag limits. Naturally, they expect to see ducks in the fall. Unfortunately, however, local hunting conditions sometimes don"t match the expectations."
While some hunters have questioned the survey's accuracy, researchers and pilot-biologists uniformly support the data. They point to scientific reviews that reaffirmed survey techniques and statistical accuracy in each of the past three decades.
Still, the disconnect between hunter experiences and survey data is troublesome, says Norrgard. "This isn"t easily explained," he says. "We believe the ducks exist, but population data isn"t gathered after the spring survey, so it's very difficult to say where ducks are going during the hunting season, from a scientific standpoint."
The DNR in Minnesota and other states are considering proposals to gather data on waterfowl in late summer or early fall.
One possible explanation for fewer fall ducks, says USFWS biologist Khristi Wilkins, is hunting pressure, which is significant in Minnesota, a state that regularly ranks in the top five for active waterfowl hunters.
"Ducks are wary creatures," Wilkins says, "They tend to seek out areas where they receive little or no hunting pressure."
Test of Time
Major changes to the USFWS survey areas are unlikely, though improvements in satellite imagery or the use of unmanned aircraft could someday help expand the survey into remote areas that currently aren't covered. For now, hunters and wildlife managers alike will count on pilot-biologists like Solberg to keep flying the traditional routes that provide an annual view of North American breeding waterfowl populations.
"It's like following in the exact footsteps of the great waterfowl pioneers," says Solberg. "We might use computers and GPS, but it's very much the same process. The fact that this survey has stood the test of time says a lot about the people who designed it, as well as the hundreds of people who continue to work to maintain and improve it."
Jason Abraham is a staff writer for the DNR divisions of Ecological Resources and Fish and Wildlife.