Mottled Mystery
Gators were the prime suspect, but habitat destruction may be the real culprit behind the decline of mottled ducks.
By Wendee Holtcamp
The Texas mottled duck population has taken a beating over the past 40 years, but no one is quite sure why. Is the population reduction due to habitat loss? Predation? Hunting? Alligators? A recent report by The Gulf Coast Joint Venture — a partnership between state and local wildlife agencies and nonprofit organizations — showed a dramatic and consistent downward trend in the mottled duck population between 1966 and 2002. Only in Texas has the population taken a swan dive; in Louisiana there exists no downward trend. “We don’t consider it a crisis yet,” says TPWD waterfowl biologist Mike Rezsutek. “But we’re concerned.”
In a night-time adventure repeated throughout the spring and summer, biologists — including Rezsutek — take an airboat through the back sloughs of J.D. Murphree WMA on the upper coast in search of answers. K.J. Lodrigue is a Texas A&M University graduate student studying whether the coast’s alligators may be a factor. From the airboat, he and the crew perform alligator rodeo — a spotlight illuminates shining reptilian eyes on the water’s surface, and as the boat inches closer, Lodrigue quickly lassoes a big one, wrangling it onto the boat. After the crew has captured several, they head back to the lab where they pump the alligators’ stomachs. Although scientific analysis awaits completion, says Rezsutek, “from what the alligator folks were able to see, mottled ducks don’t appear too often in alligator tummies, and probably are not a major source of mortality — in opposition to what many of the old timers claim.”
In drought conditions, alligators may start to impact mottled duck populations as they concentrate in scarce freshwater. Mottled duck numbers dropped by 50 percent from 2004 to 2005 — and 2005 was a dry year. Such fluctuations are within the observed range for the past few years, but the real concern is that the midwinter counts of mottled ducks have declined from highs of 50,000 - 80,000 in the early 1970s to numbers in the 17,000 - 25,000 range over the past several years. Midwinter counts don’t represent an exact count of the population, but do provide a scientific index of how well the population is faring overall.
Although more studies are needed, the GCJV report suggests that the primary cause of mottled duck decline is lowered nesting success and brood survival rather than adult survival — a number that would be affected by hunting or predation.
Both gators and mottled ducks prefer freshwater marsh, a habitat that has declined due to development and saltwater intrusion. In addition to loss of natural coastal freshwater marsh, fallow rice fields — once common throughout East Texas — provide ideal nesting habitat. But local rice farmers can no longer compete effectively with cheap foreign imports, and former rice fields are being taken over by tallow trees. Rice farming in Jefferson County — where J.D. Murphree WMA lies — declined 35 percent over the last year.
Rezsutek and colleagues will work to improve habitat — whether that means predator removal or ensuring salinity stays below 8ppt (above which is fatal to ducklings). The new USDA Grassland Reserve Program — modeled on the Wetlands Reserve Program — may provide an option to create breeding and nesting grounds. In the end, without more habitat, as Rezsutek says, “It may be that they’ve reached their carrying capacity with what we have left.”
To get a copy of the GCJV report, or if you’re interested in improving your land for mottled ducks, contact Rezsutek at Michael.Rezsutek@tpwd.state.tx.us or (409) 736-2551 x 30.
