Recently I discussed a genetic cross between different species in plants. The result was a new plant that was infertile. This happens quite often in ducks. Usually, male mallards (Anas platyrhynchos) are the reason why.
Mallard males will cross with female black ducks (Anas rubripes). Mallard males are larger and far more aggressive than their black duck counterparts. Consequently, they usurp the opportunity to breed with any black duck female they wish.
These two species are closely related enough to produce offspring. The problem is that both male and female ducklings will be infertile. Eventually, black duck populations will be depressed and there’s not a whole lot anyone can do about it. It’s not a problem in places where their ranges don’t overlap, but if breeding areas are the same, black duck populations will continue to decline.
It doesn’t end there. If male mallards and female black ducks form a bond in their winter range, this could sustain the relationship to the breeding grounds. This will result in many more black mallard hybrids. For the past 60 years or so the eastern expansion of the mallard has cut pure black duck numbers significantly.
So what about the female mallards? There’s no worry there. The mallard drake is a very sexually active critter. He’ll take care of them too.
Normally, when a wildlife species population decreases, we can relate it to human activity such as habitat destruction. In this case that might be slightly true. Well-meaning folks who feed ducks could cause range expansion as could increased grain production in some places. Food plots aren’t natural habitat.
A bigger problem might be releasing human reared mallards into the environment. Sometimes this is accidental, but often it is done on purpose. Mallards are easy to raise, and eggs are readily available, so many escape into the wild. Some start out as pets but are deliberately released as owners tire of them. Many of them escape predators long enough to mate.
Mallards are among the most adaptable of all ducks. They are found in all 50 states. These guys are comfortable anywhere a water source is available. The water need not be deep, either. Conservation of black duck habitat won’t keep the mallards from encroaching.
Mallard and black ducks naturally migrate to related environments. Both have similar diets. Also, they are both dabbling ducks. This means they usually don’t dive underwater to obtain food. They simply stick their heads underwater leaving their butt in the air.
Crossbreeding of waterfowl is a fairly common thing. I’ve highlighted the most common cross, but others occur. Mallards will cross with pintails, widgeons, shovelers, teals and gadwalls.
I have a cabin in northeastern Maine. Ranges of black ducks and mallards don’t overlap in that breeding ground. Only black ducks live there, so if little pockets like that exist, black ducks should not become extinct. Moreover, there is little agriculture in that area to lure other species in.
That means populations will remain low but dominated by black ducks. Sometimes limited food and low populations are a good thing.
A small family of black ducks
Ted Manzer teaches agriculture at Northeastern High School.