The Mallard Mystery

Mallard
Researchers remain stumped as to why mallard numbers in the Atlantic Flyway have fallen 45 percent in the past 20 years. Shutterstock/Jeffry Weymier

In 2000 the Atlantic Flyway mallard harvest peaked at 523,000 birds. However, that year marked the beginning of a steady decline to 286,000 mallards in 2017. As a result of this worrisome trend, the US Fish and Wildlife Service and Atlantic Flyway Council reduced the daily limit from four mallards to two for the 2019-’20 waterfowl season in the Atlantic Flyway. What has been happening to the Eastern population of the country’s most popular waterfowl?

At this point the official answer is that no one knows with certainty. The search now stretches from examination of historical records to the latest tools of molecular research.

Let’s begin with a fact that may come as a surprise to many duck hunters. A century ago greenheads were rare along the Eastern Seaboard. That began to change with the deliberate introduction of European mallards to game farms and hunt clubs so they could be released and hunted or shot. Large numbers of birds inevitably escaped into the wild and established breeding populations. By 1960 mallards were the most frequently harvested duck in the Atlantic Flyway. They were so abundant that regulatory agencies relied on mallard numbers alone to determine the length of the general duck season. (That practice stopped in 2000, as mallard numbers already were falling and becoming less representative of overall duck populations. Season lengths now are based on a composite of survey results for wigeon, green-winged teal, ring-necked ducks and goldeneyes.)

Another established fact holds important clues to the mystery. The decline in North American mallards is limited to the Atlantic Flyway, where numbers have fallen by some 45 percent during the past 20 years while populations farther west remain near historic highs. Any theoretical explanation for the Eastern decline will have to account for this discrepancy.

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Habitat problems always provide a logical point of beginning in the search for explanations of a wildlife population decline. In this case there is no obvious evidence of the usual suspects, such as drought, other extreme weather events or major changes in land-use patterns. Michael Schummer of the State University of New York College of Environmental Science and Forestry, in Syracuse, leads a team exploring environmental factors as potential causes of the problem. “We don’t know the mechanism,” he acknowledged. “Eastern mallards are one of the most monitored populations on the planet . . . . We have all these data, but we don’t know why they are in decline.”

Currently his group is using everything from satellite imagery to isotope analysis from collected feathers to learn more about where the birds are breeding and nesting. The goal is to identify specific local habitat factors that may correlate with decreased reproductive success.

Schummer’s group, Rescue the Eastern Mallard (which receives support from Delta Waterfowl and Ducks Unlimited), also collaborates with the University of Texas’s Dr. Philip Lavretsky, whose genetic studies have revealed some fascinating findings. His team initially focused on the complex genetic relationship among mallards, black ducks and their hybrids, but that soon led to new information about the continental mallard population.

Sudden changes in any wildlife population are often multi-factorial.

DNA samples taken from mallards collected on the East Coast a century ago proved essentially identical to DNA from current Western populations of wild mallards. However, Eastern mallards harvested from the mid-1950s on had distinctly different genetic markers, indicating that they derived from birds of domestic European origin. Today’s Eastern mallards are more distant genetically from Western mallards than are black ducks and mottled ducks.

These genetic footprints correlate with the known introduction of European mallards to Atlantic Flyway game farms in the 1900s and establish that most Eastern mallards derived from the original European stock. Those birds had been bred for domestic purposes across the Atlantic for hundreds of generations. Eastern mallards differ from wild Western mallards in form and behavior as well as genetic makeup. Studies showed that Western mallards enjoyed a small but significant advantage in one-year survival over their Eastern counterparts. Eastern birds are smaller on average and have a different bill structure said to be better adapted to the consumption of domestic grain. Hens experience a longer period of vulnerability on nests and guard their nests less vigilantly.

Interestingly, numbers of breeding Atlantic Flyway mallards in Canada have remained relatively stable while numbers have declined farther south, according to similar sampling methods. Evidence suggests that Canadian mallards populated naturally from mid-continental stocks rather than by the release of domesticated European birds, as was the case on our side of the border.

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Whatever the genetic makeup of the involved mallards, something must have changed 20 years ago to initiate the current decline. Sudden changes in any wildlife population are often multi-factorial, so biologists investigating the issue are likely looking for more than one precipitating cause. None has been definitively identified yet. However, we do know that genes among the Eastern mallard population are significantly less diverse than those among its Western counterpart, and limited genetic diversity makes any species less capable of adapting to environmental change. It’s likely that some alteration in climate, food sources, nesting habitat, predation or other factors eventually will emerge as a culprit with which genetically restricted, artificially derived Eastern mallards couldn’t cope.

It would be a mistake if our concern for Eastern mallards distracted us from the welfare of another puddle duck that has been there all along: the black duck. As mallard populations increased in the late 1900s, black duck numbers dropped sharply—by 50 percent between the 1950s and 1990s. Since then they have stabilized, although they remain below goals established by the North American Waterfowl Management Plan and have continued to decline in the Mississippi Flyway. While the exact cause of that decline remains unclear, the temporal association with increasing mallard numbers suggests competition for resources and hybridization with mallards as significant contributing factors.

We don’t have definitive answers yet, and the future of Atlantic Flyway mallards remains uncertain. Given the information and reasoning cited above, it seems likely that, as Walt Kelly’s cartoon possum, Pogo, once parodied Commander Oliver Perry: “We have met the enemy, and they are us.” We wanted more mallards on our East Coast, and we got them—without paying sufficient attention to their biological fitness or eventual impact upon other species in their brave new world. 


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