Naturespeak

February 24, 2013

Black Ducks on Thin Ice

Filed under: Uncategorized — wykes @ 8:12 pm

The wintery Detroit River flowing around Grosse Ile on a late February day was a mixed bag of scenery. A rim of shelf ice clung to the shoreline of empty docks and boathouses. Out in the channel the river moved along at a leisurely pace – open steely blue-gray water with occasional lazy cakes of ice floating by. On the Canadian side, especially in the vicinity of tree covered Stony Island, the river was full of waterfowl.

  

Hundreds of birds rode the small waves generated by the cold northern wind. Most were divers out in the deeper water of the main channel. Because they all fed in a similar style, Canvasbacks, Red-heads and a few Ring-necked Ducks formed the largest clusters (rafts). They bobbed up and down as they dove to seek water celery tubers, pill clams, and the like. Smaller congregations of dabblers hugged the near ice side of the current. Most of them were roosting on the thin ice. All were big-rumped dark birds profiled against a white background and all had the same profile when viewed from the road (this is the only way one can view ducks on Grosse Ile if one is not a resident).

Most of the birds were Mallards, but a few were not.  As a big-rumped island visitor myself, I did notice a number of darker birds in the ice flock.  These birds, appropriately called Black Ducks, stood out from a distance.  One pair remained on the ice long enough for me to capture their images and unwittingly allowed me to ponder the subject of Black Ducks. This ultimately permitted me to inflict my ponderings upon you, dear reader. Black Ducks are not rare but they are uncommon enough to warrant a second look. First of all there is the issue of identification.

The male and female are nearly identical in appearance. Both sexes are very similar to female Mallards. Unlike female mallards, however, they have a chocolate brown body with a contrasting pale (coffee-with-cream color) neck and head. The colored portion of their wing, the speculum, is iridescent purple with a black border as opposed to the same feature on a female mallard which is iridescent blue with a white border. The bill on Black Ducks tends to be olive green while Mallards sport a yellowish bill. Finally, Black Ducks have distinctive deep red-orange feet (the species name rubripes means “ruddy-footed”). I would say that this is a dead give-away except that it is very noticeable on live birds as well (note joke here).

You can’t help but notice that my Grosse Ile fowl were pretty hefty (and lazy – note the pile of droppings deposited were they rested). They were extra diligent, however, and were immediately alerted by my distant presence. Both stood up, waddled away to the open water, and swam away with their escort of Mallards.

This was a definite “pair” of birds. Black Ducks form their pair bonds during the fall and winter migration. “Hey baby, want to take a trip with me?” is the apparent pick-up line in such situations. The willing females, thinking about a romantic tryst along the sunny Gulf States quickly agrees.  One can only imagine what a female who ends up wintering on the Detroit River might say to “Hey baby, let’s sit on the Detroit River ice and look fat.” That at least some of them say “yes” to this proposition is obvious in my Grosse Ile pair.

Since the early 1960’s, this species has declined in numbers. So you could say that my pictures are allegorical in that the species is on some thin ice. Part of the blame goes to habitat destruction and harvest related concerns, but there is more going on. Mallards are being blamed by some. Because the two species freely interbreed, there has been some air time given to the idea that Mallards are slowly diluting the gene pool and that is presented as a bad – or preventable – thing. Those nasty green-heads are mucking up the picture. I’m not sure that perception is entirely correct.

On an evolutionary scale, Black Ducks and Mallards are called “sibling species.” This means that they are very closely related to each other. Genetically there is very little difference between them and, in fact, they may not quite be totally separated from each other.  One well-informed study estimates, based on the mitochondrial DNA, that they separated only 430,000 years ago (sometime during the last Ice Age). That is a drop in the time bucket when considering species formation.

Mallards have a world-wide distribution where-as the Black Ducks are exclusively North American. The Blacks are out-numbered. There are a few traits, such as a slightly later nesting season, that serve to separate the two but behaviorally they are so similar that it is fairly easy for dark-headed drake Mallards to woo unsuspecting Black Duck females into parenthood.

As is true of so many events, we find ourselves in the current age observing what may be a totally natural process. Am I saying that Black Ducks may not survive the whole species independence thing and eventually find themselves back into the world Mallard fold? Am I saying that Black Ducks are still experimental? Yes, I am. So, take your time when looking at Black Ducks because they may not be here ten thousand years from now. Perhaps I am on thin ice in making this prediction, but none of you will be around to call me on it will you?

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