6 minute read
Following The Flock
Garrett Dietz
Garrett Dietz is a public information officer in the DNR’s Office of Communications.
Each spring and fall, millions of ducks and geese grace Wisconsin’s skies as they migrate between breeding and wintering grounds. These migratory pathways span thousands of miles across North America and keep DNR staff busy year-round.
In fact, a successful fall waterfowl hunting season wouldn’t be possible without management efforts that start in the spring.
As a breeding area along the Mississippi Flyway — a migratory pathway that includes 14 U.S. states and three Canadian provinces — Wisconsin sees millions of waterfowl migrate through the state each year. Managing them is a collaborative effort among many agencies and conservation partners across the U.S. and Canada.
Taking Flight
To track birds over time, the DNR conducts a spring survey of breeding ducks to contribute to national data on waterfowl populations. Wisconsin is one of three states, along with Minnesota and Michigan, that conduct their own breeding survey.
The Waterfowl Breeding Population Survey for Wisconsin is at the core of the state’s waterfowl monitoring strategy. Flying low in a small airplane, DNR biologists count wetlands and identify waterfowl along predefined routes, called transects, to estimate breeding populations.
These efforts also involve recording every waterbody within 200 meters of the flight path. From flooded cornfields to forested wetlands, every puddle and pond along a transect is logged. The volume of water observed helps estimate habitat availability, a key piece of context for comparing breeding success over time.
“We’ve been flying the same 66 30-mile-long transects since 1973,” said Taylor Finger, DNR game bird specialist. “We follow the same protocols used by the U.S. Fish and Wildlife Service and the Canadian Wildlife Service to ensure our data contributes directly to national and international waterfowl management decisions.”
Flying at nearly 100 mph over the ground, it’s possible these eyes in the sky might miss some waterfowl under trees or hidden in wetlands along a transect. That’s why the DNR also “ground-truths” the tallies.
This process involves sending trained staff and volunteers to be boots on the ground, walking a defined grid through a transect and counting all waterfowl observed. The ground truth number is then compared to the aircraft-observed tally and used to determine a visibility correction factor that can be applied to all aerial counts to ensure the most accurate data possible.
This past spring, aerial survey results estimated Wisconsin’s 2025 breeding mallard population was 149,568 birds, a 2% increase over 2024. This number is especially important because it helps inform hunting season regulations at the national level.
Why Mallards Matter
Mallards are the most common and widespread duck in North America, present in myriad habitat types. Because of this, their population health serves as a proxy for many other species of dabbling ducks (those that feed at the water’s surface or just below, in contrast to diving ducks).
As such, the U.S. Fish and Wildlife Service reviews national mallard breeding population data to determine the season length and daily bag limits for fall waterfowl hunting. The mallard data collected by the DNR is submitted to the USFWS to contribute to this population count.
“The theory is pretty simple,” Finger explained. “If mallards are doing well, chances are most other ducks are also doing well. If we see their numbers dip significantly, that’s a red flag for all dabbling ducks across the country.”
Though mallards dominate management models, Wisconsin boasts quite a few other species of breeding waterfowl. Together, mallards, wood ducks, bluewinged teal and green-winged teal make up about 70% of game waterfowl in Wisconsin.
Big On Bird Banding
Another key component of the state’s monitoring efforts is bird banding. Wisconsin has one of the largest banding quotas in the nation, with annual goals to band 4,100 Canada geese, 4,000 mallards and 1,700 wood ducks.
Originally designed to track migration routes, waterfowl banding now plays a critical role in harvest management.
“We look at recovery rates from hunters to assess population health,” Finger said. “For example, if we start receiving an influx of adult hen harvest reports, it could mean adjusting regulations to protect our breeding stock for future years.”
Newer technologies like GPS backpack transmitters have also
opened new windows into duck behavior. From 2021 to 2023, researchers across the Great Lakes region outfitted more than 600 mallards with transmitters to study habitat use, migration timing and nesting success.
Drones Pose Promise
While traditional surveys still rely on human observation, new tools may enhance future waterfowl monitoring. DNR staff are exploring the use of drones to supplement ground-truthing efforts, offering higher-fidelity counts with greater efficiency.
“Instead of sending a few people into a wetland for hours, we could launch a drone, fly over the same area, and get accurate bird counts in minutes,” Finger said. “It would save time and could improve accuracy.”
Limitations like battery life and federal aviation regulations mean drones won’t replace aerial surveys soon, but they offer exciting potential for validating data or surveying difficult-to-access wetlands.
Migration And Habitat
While exact migration numbers are hard to pinpoint, it’s clear Wisconsin plays host to millions of waterfowl each fall. On Green Bay alone, biologists regularly observe tens of thousands of scaup staging during migration. And along the Mississippi River, up to 75% of North America’s canvasbacks may stop to rest and refuel.
“It’s not an exaggeration to say millions, maybe even tens of millions, of birds pass through the Great Lakes region each fall,” Finger noted. “Even if we can’t count
every single one, we know they’re using the flyway.”
Management doesn’t stop at monitoring breeding, migration and hunting. Wisconsin’s Waterfowl and Wetland Habitat Conservation Plan also outlines methods to conserve and protect crucial habitat. The plan utilizes a model to rank watersheds by their importance for breeding waterfowl.
This model helps guide the DNR when making decisions on how to allocate funds from sales of the state’s Waterfowl Stamp. Weighting breeding habitat more heavily than fall migration habitat means restoration work directly supports the long-term reproductive success of our most prominent waterfowl species.
“We want to ensure that the places we invest in will actually move the needle,” Finger explained. “The goal is to put our habitat dollars where they’ll do the most good for the future of ducks and geese in Wisconsin.”
Hunters and nonhunters alike can support waterfowl conservation by purchasing a Wisconsin Waterfowl Stamp.
“Purchasing a stamp is the single most effective way people can support waterfowl conservation,” Finger said. “Even if you never hunt, buying a stamp helps ensure we have birds, wetlands and public recreation opportunities for everyone to enjoy.”
Learn More
Visit the DNR's Waterfowl Management webpage for a wealth of information about waterfowl management in the state, including a link to results from waterfowl population surveys.
For waterfowl hunting information, check the DNR website.
