Waterfowl in the Bayou State

Frank Rohwer  |  5/5/2005 6:46:03 PM

Frank C. Rohwer

An abundance of opportunities for fishing, bird watching, boating and hunting lends credence to Louisiana’s claim as a “sportsman’s paradise.” If you are one of those enthusiasts who anticipates the 3 a.m. alarm, long drives, boat rides on dark and cool mornings knee-deep in mud and water, then you know that Louisiana is paradise for wildfowlers. The Bayou State is right at the bottom of the migratory funnel known as the Mississippi Flyway, one that tens of millions of ducks follow as they head south each fall. The state’s coastal marshes, bays, bayous, beaver ponds, rice fields and flooded bottomland timber provide the wintering sites for millions of waterfowl. That makes for many opportunities for Louisiana residents and visitors to partake in duck watching or duck hunting.

The national scorecard on duck hunting bears witness to the abundance of ducks and the dedication of Louisiana wildfowlers. An average Louisiana duck hunter bags almost 25 ducks a year. Not only is that the highest harvest of all 50 states, but it is about four times the average yearly harvest of other U.S. hunters. Clearly, Louisiana is a great place for ducks and those who love to pursue them.

Pothole Habitat
There are scores of biologists working to assure an abundance of waterfowl to support the wildfowling tradition in Louisiana and other states in the migratory pathway. Duck populations fluctuate considerably, but mostly in response to conditions on the breeding grounds, especially wetlands. Most ducks that winter in Louisiana breed in what is known as the “pothole habitat” in the northern Midwest, especially North and South Dakota and the Canadian prairie provinces of Manitoba, Saskatchewan and Alberta. Potholes range in size from more than 40 acres to room-sized puddles. The smaller ponds are the most productive for ducks because they have a lot of edge, which is where you find the high protein insects that are food for breeding females and their fast-growing young. Because it is impossible to manage the water levels in ponds, biologists can only hope for abundant summer rains and winter snows. The current abundance of waterfowl reflects a seven-year period (1994-2000) of plentiful water, the longest continuous span of good breeding ground conditions since 1950, when the monitoring of wetlands began.

The major impediment to duck production on the prairies is high levels of nest loss to predators. The fate of most duck eggs is to be eaten by a red fox, raccoon or skunk, the three most serious egg predators. Of those three, the fox is the most devastating on ducks for two reasons. First, foxes are good at capturing incubating females at their nest. Most dabbling ducks, such as mallards, teal, pintail, gadwall (gray ducks) and wigeon, nest in the uplands. Their nests are on the ground hidden in grasses and small herbaceous plants. Foxes can track the scent upwind until they get close to the nest, then when the female flushes, the fox grabs her out of the air. The second trait of foxes that makes them particularly serious predators is that they cache eggs. This behavior is like squirrels with acorns. The fox removes eggs, one at a time, and hides them in the grass some distance from the nest. The eggs are hidden unbroken and typically not eaten until the following fall or winter.

Predator Triad
The fox-skunk-coon triad of predators has greatly benefited from the changes that settlers made when they reached the prairies. Raccoons are completely new to the prairies, and only extended their range to this part of North America after 1940. Red fox used to be rare, but they have replaced swift fox, which are now an endangered species. Skunks have also increased in numbers because of plentiful winter foods, such as sunflower seeds, and the ready availability of den sites in old buildings and rock piles created by farming.

In some areas fewer than 5 percent of duck nests actually produce hatched eggs, so it is not surprising that most waterfowl management in the prairies is focused on improving nest success. While there is consensus that nest success is the limiting step to duck production, there is little agreement on the best management strategy to increase nest success. In the past couple of decades, the prevailing strategy was to make nests inaccessible. The most common form of management involved planting farmland back to grassland. The idea is to spread out the nests so they are hard to locate. With intensive agriculture, ducks are forced to concentrate nests in the remnant strips of cover that surround ponds or are along dirt roads. These strips are small enough that a predator can find nests easily.

Restoring grasslands is an effective approach, but it is more complicated than wildlife biologists initially expected. These small patches of grass, 40 to 200 acres of grass, are also ideal home ranges for predators, so nest success does not improve to levels that allow substantial duck production. It takes much bigger patches of grassland to improve nest success substantially. Wildlife managers do not have the funding to purchase the land necessary to convert back to something approximating the prairies. In 1985, however, the U.S. Department of Agriculture took a new tack with farm subsidies and decided to pay farmers to take highly erodible land out of production and grow grass instead of crops. The effect on wildlife has been significant. In the Dakotas there are now many millions of acres of grassland in the Conservation Reserve Program (CRP), and nest success in CRP areas is often 30 percent—a great number for ducks.

Lower Predation
Meanwhile, wildlife researchers are looking at other ways to increase duck production by lowering predation rates. One way is to make nests more inaccessible. Nest sites can be made by rolling grass between wire to make a tunnel. Grass and straw go inside the tunnel for nesting material, and the structure is mounted on a pole over the wetland. This safe nest site is acceptable to mallards, which have an 80 percent hatch rate in these structures. The down side is that nest tunnels require maintenance. One way to avoid having to reroll the grass in the wire is to use Astroturf. But mallards, like pro football players, prefer the real thing.

To avoid high maintenance, some managers have created nesting structures that grow their own cover. During a drought year, a 36-inch concrete culvert can be placed on end in the middle of one of the shallow potholes and filled with dirt (Figure 1). The culvert acts like a giant planter for weeds and grasses that serve as nesting cover, which is quite attractive to female mallards and Canada geese. The inaccessibility to mammalian predators means the females that nest on the culverts have an excellent chance to hatch their eggs. The large size and weight of culverts, however, mean that big equipment is required to dig them into dry pond beds, stand them upright and fill them with soil. Moreover, culverts are like the Titanic, not as durable as initially expected. As ponds thaw in the spring, the ice first melts at the shoreline. Then each pothole has its own iceberg. With a strong wind these smaller versions of high seas menaces can knock over the culverts.

Creating nesting islands is another way to make nest sites safer. Ducks are naturally attracted to islands in large ponds, where they avoid most predators except mink. The problem with creating islands is that it is expensive to move dirt, even though it can be trucked on top of the ice in winter. Another problem with islands is that they tend to wash away quite rapidly. This problem is sometimes aggravated by Canada geese, which graze islands so heavily they remove most of the protective plant cover.

The general lack of success with getting nests out of harm’s way has caused some to reconsider an older form of management—reduction of the predators. LSU AgCenter researchers have been involved in assessing the efficacy of trapping predators. The question was whether a trapper could remove enough predators from a large block of land (16 square miles) to improve nest success. A nonprofit waterfowl organization called the Delta Waterfowl Foundation contracted to have four 16-square mile blocks trapped. An AgCenter research team found more than 3,000 duck nests both on and off the trapped blocks. Nest success on the trapped blocks was a phenomenal 45 percent compared to 17 percent on the untrapped blocks. Songbird success was not altered, but the success of the ducks that nest in the wet margins of the ponds, such as redheads and canvasbacks, was doubled. In a subsequent collaborative Delta Waterfowl/LSU AgCenter project, researchers evaluated trapping of even larger chunks of habitat, 36-square-mile units.

Trapping these large units yields even greater duck production because the elevated nest success is extended to such a large area. Trapping proved so effective that some management agencies are slowly beginning to use this approach to waterfowl management. Of course, predator reduction is a much more controversial form of management than habitat restoration. However, waterfowl managers point out that hunters contribute millions of dollars each year to restore waterfowl habitat, yet much of this land produces few ducks because of the exceptional predation levels. Lethal predator management can never remove all the predators, but it allows ducks to achieve greater nest success.

LSU AgCenter researchers will continue to evaluate the efficacy of techniques used in waterfowl management. An important part of this is finding ways to enhance nest success on the prairies, knowing that the ducks from the Dakotas spend as much time in Louisiana in the winter as they do on their prairie nesting areas in the summer.

Two other LSU AgCenter research projects are these:

Investigation into why pintails have not recovered to record population levels like other ducks.

Also, AgCenter researchers have discovered that the effect of hunting on mallard numbers has been overestimated because biologists have gathered incorrect duck age ratios data. They are working on corrections for the age ratio data. This research will have an immediate impact on harvest regulations that affect all of the Mississippi Flyway. It appears that the faulty age ratio information was causing conservative regulations, so revised data should not involve any belt-tightening restrictions on harvest and may, in fact, result in more field days for Louisiana hunters.

Frank C. Rohwer, Associate Professor, School of Renewable Natural Resources, LSU AgCenter, Baton Rouge, La.

(This article appeared in the spring 2002 issue of Louisiana Agriculture.)

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