Guest Author - Kimberly Weiss
Finally, a weekend that was warm enough to go birding.
Unfortunately, that meant only that the wet stuff falling from the sky was rain, not snow. Had it not been approximately 33 degrees Fahrenheit (thatís a frigid 1 degree Celsius), we would have had to get the plow out in the New York City Area.
Anyway, it stopped raining for a little while, so I made it down to one of my favorite natural areas. There werenít many birds there, but I did see one of my favorites: the black duck mallard hybrid.
A hybrid is an animal (or plant, for that matter) whose mother and father were different species. The most famous hybrid animal is the mule (horse and donkey), but other hybrids include the liger (lion and tiger) and swoose (swan and goose). Mutt dogs are not hybrids; their parents are different breeds, but both are the same species. Mutts are fertile, where most hybrids are not.
A black duck X mallard hybrid male has the dull feathers of a black duck with just a stripe of green on his head. Some may have a suggestion of the mallardís black and gray striped back, but overall , the ones Iíve seen look more like black ducks than their more colorful cousins.
Why do these two species hybridize so often? For one thing, they are closely related. The two species split fairly recently, evolutionary biologists believe. They are the same genus (Anas).
At one point in time, mallards and black ducks did not mix as often as they do today. Black ducks were found in salt marshes and along the US eastern coast, while mallards were ducks of fresh water in the midwest. But the mallard population has been increasing, and mallards are appearing in the ecosystems once dominated by the black duck.
I did a paper on black duck/mallard hybrids many years ago, and I still remember one of the studies in a scientific journal article I used as a reference. Unfortunately, I could not find a link to it online, but I will summarize as best as I can recall.
In this study, a group of black ducks and mallards were put in an enclosure with a very desirable ledge to sit on. The researchers noticed that the black ducks rarely got to sit on this ledge. If one of them did manage to get a spot on it, a mallard would soon come and push him off. They also noted that while both species had courtship routines and formed pair-bonds with a female, the mallards would mate with other females as well, sometimes forcefully. (These birds would not make good wedding-cake toppers!) Overall, the mallards were found to be much more aggressive than black ducks, both sexually and otherwise.
The larger size of the mallard population and the aggression and promiscuity of the mallard males may be putting black ducks in danger of extinction. If mallard males continue to mate with black duck females, there may be no more purebred black ducks in the future.
Fortunately, that day is not imminent. But researchers are very concerned about the black duck population, although they feel habitat loss is a bigger concern than hybridization.
I find it heartwarming that despite their different appearance, the hybrids Iíve seen have been accepted by their purebred peers. They mix in naturally, eating and swimming with the rest. This is a situation where human beings can learn something from the ducks.