Recently, a hunter, who knew that I had studied black duck-mallard interactions for the past 35 years, asked what we are “going to do about those goddamn mallards. If they keep it up, there’ll soon be no black ducks left.”

He referred to the widely held belief that mallards are the cause of the black duck’s population decline, a concern that dates back to the 1960s when some biologists warned that the eastward expansion of mallards into traditional black duck range could eventually lead to the black duck’s demise.

The warning was enthusiastically and widely embraced. It was based on the idea that genetically dominant mallards would mate with the black ducks, effectively seducing the species out of existence. Over time, biologists speculated, a genetically pure black duck would all but cease to exist.

The idea possessed an element of truth. Blacks and mallards – two closely related species – are known to interbreed and produce hybrid young. This occurs in two ways. Male mallards sometimes rape female black ducks. Blacks may choose mallards as mates. There is no question mallards pose a genetic risk to black ducks.

A related factor involved habitat. In parts of Ontario black ducks began declining at the same time mallards began increasing, the latter occupying wetlands formerly used by blacks. Some suggested more highly aggressive mallards were driving black ducks from their traditional breeding grounds. Some further contended this prevented black ducks from breeding, at least to their maximum potential.

The net effect suggested the black duck faced a double-whammy. Black duck genes were being diluted, indeed overwhelmed by over-sexed mallards, and the genetically pure blacks that survived were prevented from breeding or forced into inferior habitat where production was minimal.

The two perils were aggressively promoted as the leading causes of the black ducks’ decline. But few asked whether the biological double-whammy posed a realistic threat to black ducks. The answer is that nobody knows for certain.

This becomes evident when considering the complex issue of genetics. We know the two species share a close evolutionary background and genetic relationship. They come from common ancestral stock but beyond that we are left largely with speculation. For example, we do not know their geographic origin (i.e., North America or Europe/Asia), and we do not know if the archetype ancestor looked more like a black duck or mallard.

We know there is today a greater genetic variation among the populations within each species than between some populations of the two different species. Even calling them separate species is a stretch. The main criterion for being a distinct species is reproductive and genetic isolation from other species – in other words, one species does not interbreed with another. But mallards and black ducks interbreed and their hybrids not only survive, they successfully breed among themselves and with each parental species. One might argue that such closely related birds are simply geographically distinct/isolated populations of the same species.

There also is considerable speculation about the black duck-mallard evolutionary relationship. One possible evolutionary scenario goes something like this. Mid-continent mallards were forced southward by advancing glaciation to the Gulf of Mexico where they found refuge. Most mallards returned to their grassland habitat when the glacier receded, but a component remained in the Gulf. Some, like the mottled duck, adapted to the Gulf’s freshwater marshes and lost their tendency to migrate. Another component moved northward along the Atlantic Coast, adapted to the tidal and forested habitats of the northeast, and became the black duck. It may be that the black duck later moved along the St. Lawrence River westward to approximately the Mississippi River, halting before reaching the grassland domain of the mallard. I stress that no one knows for sure.

The western component of the continental black duck population would appear to have been more vulnerable to the influence of the much more numerous mallard than the eastern population. This suggests that black duck populations would be less impacted as one goes from west to east. There is some evidence to suggest this is the case.

For example, coastal black ducks have evolved ecological preferences different from the mallard. They are attracted to and more tolerant of brackish/salt water. This reduces the likelihood of encounters and interbreeding between the species. But one of the most curious differences involves geography. Something quite different occurs as one goes from west to east. Most mixed pairs in the western part of the black duck’s range involve male mallard-female black duck pairs. Along the coast the opposite situation prevails. It is likely that some black duck populations, particularly in the western part of their range, are indeed being negatively impacted by mallards, but this is not necessarily the case elsewhere.

Thus, the hybridization issue remains unresolved. Attempted rape is dramatic to see but rarely results in females being inseminated. So-called mixed pairs also occur but not to the extent that early studies suggested would eventually occur. Regional differences cast doubt on the general application of regional studies. Recent studies further suggest that black ducks are not universally competing with mallards for breeding habitat. Eastern black ducks may be stable and possibly even increasing. Also, some black duck populations are declining in areas where there are no mallards.

Thus, the biological evidence suggests the predicted demise of the black duck due to hybridization and competition with mallards has been exaggerated.

Unfortunately, many hunters and waterfowl-management types still blame mallards. This is a dangerous perception because it detracts from other potential problems involved in the black duck’s decline, factors such as the declining quality of wintering habitat and hunting mortality. There is increasing evidence pointing to over-shooting as a significant factor in black duck declines. But the relative roles of habitat, over-shooting and mallards are poorly understood in the population dynamics of black ducks. Caution is advisable in drawing hard conclusions.

To my mind, the mallard has become a distraction, perhaps a diversion, in discussions over how best to sustain or increase black duck populations. This is especially true in debates about the impact of hunting. Many biologists who refuse to consider hunting as an important factor in declining duck populations have strongly embraced and promoted the mallard as the primary player in the black duck’s decline. This leaves the erroneous impression that science has the evidence to conclude this. Unfortunately, the hunter is caught in the middle.

Isn’t it time to cast the black duck-mallard issue in a more balanced, biological light?