Study: Spring Floods Good for Handsome Wood Duck

COLUMBUS, Ohio — Springtime flooding by rivers and streams — normal and natural but limited now by dams and other flood-control measures — helps keep nesting wood ducks safe and lets them successfully raise more young, says a study by scientists in Illinois and Ohio.

Wood ducks suffer more nest predation and as a result less nesting success when the floodplain forests they nest in don’t flood, the study reported.

The finding, by Charlotte Roy Nielsen of Southern Illinois University Carbondale (SIUC) and Robert Gates of Ohio State University, suggests that modern flood control, done to help people and structures in floodplains, may hurt birds that nest in such places: not only wood ducks but also many songbirds.

“Bottomland hardwood forests have always functioned best with more modest and sporadic but seasonally predictable flood events. This is what makes them so productive,” said Gates, a wildlife ecologist with Ohio State’s School of Environment and Natural Resources (SENR) and Ohio Agricultural Research and Development Center (OARDC).

Now, however, “Flood-control efforts tend to widen the amplitude of seasonal flood events,” he said. “Bottomlands may be flooded briefly if at all during most years but experience catastrophic — to both human and wildlife communities — flooding every decade or so.”

Seasonal, not-too-serious flooding likely helps birds several ways, Gates and Nielsen said. It might keep predators away from nest trees — imagine a castle with a moat all around it; might make predators move or drown; and might give predators alternative prey: fish and frogs, for example.

Nest predation, other studies have shown, ranks as the single biggest factor affecting songbird and waterfowl populations.

Wood ducks typically nest near water. They nest in holes in trees and also in boxes that people put up.

The study looked at wood duck nests in a bottomland hardwood forest in Illinois. The site lay next to the Mississippi River. No predation took place during flooding, but 20 percent of the nests were attacked, with eggs, young or both wiped out, when the land was dry.

The scientists also analyzed the years that led up to the study, 1995-2002, comparing flooding and wood-duck nest predation, and came to the same conclusion: that nest predation — typically by raccoons and black rat snakes — falls when flood waters rise.

“We’re not saying take out all of the dams and flood-control levees,” Gates said, “but we can use the physical infrastructure to manage these systems better. Not at the extremes — complete or no flood control — but at more intermediate levels of intensity that allow for some restoration of natural flooding patterns.”

Such patterns, when and where possible without affecting people adversely, “will ultimately sustain the productivity of bottomland hardwood forests for humans and wildlife,” he said.

Flooding enriches bottomland soils by bringing in nutrients and organic matter. The land tends to make for excellent farming.

“This is an example where wildlife and agriculture really share a common interest,” Gates said. “Isn’t it wiser to build permanent infrastructure — houses, industry, etc. — in places that don’t need to be protected by flood-control systems, so that floodplains can be productive for both agriculture and wildlife?”

“Any restoration of flood regimes is a long-term goal, not an immediate one, and human interests will certainly weigh heavily in any decisions,” Nielsen pointed out.

Now a wildlife ecologist in SIUC’s Cooperative Wildlife Research Laboratory, Nielsen was a doctoral student at the University of Missouri-St. Louis when she teamed with Gates on the project.

The study appeared in a recent issue of the bird-science journal The Condor.

The St. Louis Zoo, the Delta Waterfowl and Wetlands Research Station, and the Sigma Xi Grants-in-Aid of Research Program gave funding support for the research. Sandpiper Technologies, California, provided a grant for equipment.

A special video surveillance device, Sandpiper’s TreeTop Peeper II, aided the work. Consisting of a tiny video camera, a pole to mount it on that telescopes up to 50 feet high, a receiver and a monitor, it let the scientists watch the nests with no need to climb up the trees.

Populations of the wood duck, native to only North America, fell dramatically in the late 19th and early 20th centuries. Gates cites habitat loss — specifically, the clearing of Eastern floodplain forests, especially near cities — as a critical factor in the decline, while Nielsen notes the added pressure of unchecked market hunting.

Since then the wood duck has rebounded thanks to wetland restoration, the maturation and regrowth of Eastern forests, and the regulation of sport-hunting harvest. The continent’s population stands at 4.6 million birds, says the National Audubon Society.

Other floodplain-nesting birds, to name a few, include the bald eagle, acadian flycatcher, cerulean warbler and prothonotary warbler.

“Floodplain forests provide some of the most diverse assemblages of birds in North America,” according to a 2006 report by the U.S. Fish and Wildlife Service and U.S. Geological Survey. “Unfortunately, because of floodplain protection projects, the ecology of many rivers ... has changed, potentially influencing avian [bird] floodplain abundance and diversity.”

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Editor: Photo by Dave Menke, U.S. Fish and Wildlife Service, available at http://www.ag.ohio-state.edu/~news/story.php?id=4096 or http://images.fws.gov/default.cfm (image 9 after entering “wood duck” under “Quick Search”).