A duck is a duck, right? Well, yes, but when one duck mates with a duck of another species, there’s the risk that one of the original species could cease to exist. And then that duck is a duck no more.
But who cares? A new, hybrid duck will emerge, and that duck is a duck, right? Maybe over geological time that would be true. But in a natural world affected by human activity, ecologists and conservationists worry that hybridization can upset ecological balances and undermine the survival of species involved in such a blend. Although not a problem yet, a study published Thursday in The Condor: Ornithological Applications suggests the riddling possibility that two duck species forming a hybrid species could one day leave us with less diversity among North American ducks.
This study is the first to assess the rate at which mallard and Mottled Ducks are combining into hybrids in the western Gulf of Mexico region of the United States. Their results highlight important questions about the interbreeding of species: How much of it is nature doing its own work? How much of it is influenced by humans? And at what point should we be concerned?
You’ve probably met the mallard — green head, frequents city parks, gobbles up your tossed bread, migrates (generally) and likes water of all kinds but isn’t too keen on coastal waters. This duck is perhaps the most common in the world. In winter, you can find it in swamps, marshes and estuaries along the Mississippi Valley.
The Mottled Duck doesn’t migrate. It is primarily coastal, favoring brackish waters along the Gulf Coast from Florida to Texas. But dams and oil and gas pipelines are drying and fragmenting their habitats.
On occasion, the two duck species meet and mate. That shouldn’t seem like a bad thing. But hybridization has nearly wiped out bird species in the recent past. Once the Golden-winged Warbler ranged from the upper Midwest down to the Appalachian Mountains and into eastern South America, depending on the season. But then the Bluewinged Warbler moved into its habitat and nearly bred it out of existence in many areas. Today, the rare bird’s last stronghold is in Minnesota.
Conservationists have wondered if a similar scenario could play itself out with these ducks.
In Florida, feral mallard ducks, released from game farms, have quit migrating and begun breeding with native, non-migrating Mottled ducks. There, almost a tenth of the Mottled and mallard ducks are actually hybrids, which is concerning if you wish to preserve the genetic lineage of Mottled Ducks.
To test whether Mottled ducks were at risk of being hybridized too much in other parts of their range, Sabrina Taylor, a geneticist and behavioral ecologist at Louisiana State University and Agricultural Center and her team analyzed DNA from blood samples and carcasses of mallard, Mottled and hybrid ducks in Texas, Mississippi, Alabama and Louisiana. The researchers concluded that the current hybridization rate — between 5 and 8 percent — was low enough not to be a concern.
Part of this recommendation comes down to the different behaviors and habitats of the ducks in Florida versus the western Gulf. What’s a problem in Florida may not be one in the western Gulf, where mallards and Mottled Ducks have fewer chances for close encounters of a sexual kind.
The other reason not to worry yet, Taylor said, is that some hybridization is expected as part of the evolutionary process, although she questions what’s normal and what’s exacerbated by humans, which could create cases where hybridization goes too far.
This is a possibility for the ducks in the Gulf only if more mallards are released, or if Mottled Ducks seek out new homes near mallards as their habitat continues to disappear. Taylor’s work may provide a baseline for monitoring trends in the future. And for conservation, the conventional rules still apply.
“The best thing anybody can do for species, no matter what the threat is, is try and preserve habitat,” Taylor said.
So is a duck a duck?
Taylor said a student of hers put it best: “The whole idea of speciation is like a mountain range. It’s easy to tell the differences between peaks, but saying where one starts and another begins is very difficult.”