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50% Decline in Mallard Population Sparks Research Efforts

Scientist: ‘We don’t know the mechanism' that is causing the drop
10/16/2019

The U.S. population of eastern mallards has dropped by 50 percent in the last 20 years; researchers are trying to find the reason for the decline.  Photo by Ryan Chelius, ESF

By Claire B. Dunn

The U.S. population of eastern mallards - dabbling ducks with distinctive green heads - has plunged inexplicably by 50 percent in the last 20 years, causing scientists to launch research into the birds' productivity, changes in their habitat and their genetic diversity.

Long-term data collected along the Atlantic Flyway indicates the birds' numbers are falling dramatically, but scientists cannot explain why.

"We don't know the mechanism for the decline," said Michael Schummer, a faculty member at the SUNY College of Environmental Science and Forestry (ESF) in Syracuse, New York.

Schummer and several partners have responded to the changes in the population with a research effort called Rescue the Eastern Mallard. He said the challenge highlights an urgent need for humans to address biodiversity loss and devise ways to accommodate wildlife in developed areas.

"We have to get this one right," he said. "Eastern mallards are one of the most monitored populations on the planet. We band thousands of them and recover lots of them every year. We fly planes over to count them, we get on the ground and count them. We have all these data, but we don't know why they are in decline.

"If we don't figure this one out, we're in trouble," he said. "We have imperiled species in faraway places that are much more isolated. Here, we have an opportunity to answer some important questions about what happens when even common species start to decline. We are working in one of the most populated places on Earth, so we have access to lots of birds and data. If we can't find a way to keep animals with us in this urban environment, where is it going to happen?"

The Schummer Lab for Waterfowl and Wetlands Conservation at ESF is partnering with Delta Waterfowl and Ducks Unlimited. ESF is launching a grassroots fundraising effort to support the research. The scientists will use innovative techniques to analyze elements locked in mallard feathers to understand where eastern mallards are hatched. High-resolution satellite imagery helps researchers understand how changing landscapes influence the number of mallard ducklings produced. And new genetic technologies and techniques enable them to determine the genetic diversity of mallards regionally.

Understanding where ducklings hatch will provide vital information about the mechanisms of eastern mallard decline. Researchers can tease out this detail by examining feathers from ducks harvested through the U.S. Fish and Wildlife Survey's Parts Collection Survey. Flight feathers help determine each bird's species, sex and age. In addition, each flight feather contains a type of chemical signature -stable isotopes that are influenced by regional patterns that produce a specific map, or isoscape, that provides a relative understanding of where the duck was produced.

Studying changes in landscape could help explain population changes. Several states along the flyway conduct an annual breeding waterfowl survey on more than 1,000, 1-square-kilometer plots from New Hampshire to Virginia. This gives wildlife managers an archive of location-specific data on changes in mallard abundance. The decline in eastern mallards was detected using this survey; now researchers can determine what types of landscapes around these plots result in increasing, decreasing or stable mallard breeding pairs.

The question about genetic diversity involves the decades-old practice of bolstering mallard populations by releasing birds that were bred on game farms.

"It might be surprising to learn there are two types of mallards in North America - those of wild North American origin and those of European origin," Schummer said.

From the 1920s to the 1960s, conservationists bred and released mallards to supplement the wild population. But those birds were of European descent, and Schummer refers to them as domestic ducks. At least 250,000 such birds continue to be released annually along the U.S. Atlantic Coast.

Preliminary research using state-of-the-art genetic analysis by a collaborator, Dr. Philip Lavretsky at the University of Texas El Paso, suggests that most mallards along the U.S. Atlantic Coast are now of domestic ancestry. Schummer believes wild mallards might exist in the Atlantic Flyway but are mostly restricted to portions of Canada where they colonized eastward from the western prairie provinces.

The influx of domestic genes has resulted in a loss of genetic diversity that might hamper the birds' ability to adapt to change. The research team is collecting DNA from mallards throughout the Atlantic Flyway to determine the relative contributions of wild and domestic mallards to the breeding population and to duckling production.

As duck hunting season approaches throughout the Northeast, Schummer stressed the importance of solving the mystery of mallard decline.

"We are going to continue to gobble up wildlife habitat. We have to find a way to coexist with wildlife," he said. "If we can't get this one right, how are we going to get anything else right?"