by Matt Young

The biological needs of ducks change as the seasons progress. Here's how to adapt your hunting strategies to match these shifts in the birds' behavior

Migratory waterfowl are among the most fascinating and complex creatures in the natural world. While some other game birds may be warier or live in more inhospitable terrain, few, if any, are as transient and unpredictable as ducks and geese.

Just when waterfowl appear to have settled into reliable patterns of activity, hunting pressure or weather changes will cause them to alter their feeding and roosting habits. In other cases, great numbers of ducks can suddenly appear or vanish overnight following a strong cold front or heavy rains. In reality, unraveling the mysteries of duck behavior is a never-ending quest for waterfowlers, which, of course, is what makes the sport so challenging and rewarding.

Waterfowl biologists also dedicate their lives to understanding waterfowl and their habitats, except they are guided in their efforts by science rather than relying solely upon personal experience. Having completed years of rigorous study and training at universities and in the field, they know the many complex behaviors exhibited by waterfowl throughout the year.

Of particular relevance to hunters are behavioral changes occuring among ducks during the fall and winter that influence where the birds go, what they eat and how they interact with other waterfowl. To learn more about these biological events and how they relate to hunting, Ducks Unlimited interviewed several accomplished waterfowl biologists. Incidentally, all of these duck experts are diehard waterfowlers themselves, making their insights particularly valuable to hunters.

Early Fall (Sept. 1 - Oct. 15)

By late August and early September, many ducks vacate smaller wetlands used during the breeding season and congregate with other waterfowl on larger marshes and lakes. During this fall staging period, individual birds organize with others of their own species into larger flocks in preparation for migration to their wintering grounds.

Some of the finest waterfowling of the year is available in early fall on major waterfowl staging areas across North America. Randy Renner, manager of conservation programs at DU's Great Plains Regional Office in Bismarck, North Dakota, says waterfowl stage in greatest numbers on wetlands in areas with an abundance of preferred foods. "Waterfowl have to consume large quantities of food in early fall to replace nutrients depleted during the summer molt and to acquire fat reserves for fall migration.

Just like athletes preparing for a big game, ducks load up on carbohydrate-rich foods to provide them with the energy they will need to migrate long distances. Across the prairies, many mallards and pintails seek out wetlands in intensively cultivated regions, where they have greater access to high-energy crops, such as barley, peas, lentils, wheat and corn. Other species like wigeon, teal, canvasbacks, redheads, and scaup predominantly feed on submersed aquatic plants, seeds, or invertebrates, so you'll find concentrations of these ducks on staging wetlands that are rich in these natural foods."

Another essential biological need of staging waterfowl is secure wetland habitat where the birds can safely roost at night and comfortably loaf and preen during the day. Dr. Scott Stephens, director of conservation planning at DU's Great Plains office, spends long hours scouting for wetlands being used by large numbers of ducks as "day roosts." "I'm not sure why, but ducks will visit certain wetlands during the day and then use other wetlands to roost at night. They seem to use these habitats as staging areas before going on foraging bouts in the fields and also as resting areas during the day.

"Last season, I located a large concentration of mallards on a wetland and waited there until sunset to make sure they weren't roosting there during the night. Sure enough, after sunset every bird picked up off the wetland, flew about a mile and spiraled into another wetland to roost.

"The next morning, when we returned to the first wetland before dawn, we didn't flush a single duck," Stephens continues, "but as soon as shooting light arrived, a steady stream of birds started coming back from the night roost. They were so intent on using our wetland that we hardly had time to pick up our birds before another flock would set up downwind of the decoys. One of the biggest advantages about hunting these areas is that ducks use them throughout the day, whereas birds often only use night roosts before and after shooting hours."

According to Stephens, ducks often use different types of wetlands during the day versus at night. "Mallards and pintails frequently use fairly open wetlands with little emergent vegetation as day roosts, perhaps because they can see potential predators better. In contrast, night roosts are generally wetlands with more emergent vegetation, such as bulrushes or cattails, where ducks can tuck themselves away in pockets of thick cover."

Stephens says day roosts can provide productive hunting throughout the fall as new ducks arrive from the north. "These places will often fill up with new ducks when a major migration is happening. It pays to check them for new arrivals before and after major frontal passages."

Mid to Late Fall (Oct. 16 - Dec. 15)

The middle of October is a time of transition for waterfowl. The first major snowstorms and Arctic blasts of the year begin to plunge across the Canadian border, and rapidly declining day lengths and progressively colder weather trigger the migration of waterfowl from the breeding grounds. Waterfowlers in mid-latitude states live for this time of year, when every major cold front can bring new flights and hot shooting.

Mike Checkett, a Missouri native and regional biologist at DU national headquarters in Memphis, says most waterfowl migrate primarily in response to food availability. "Ducks that feed largely on aquatic vegetation, seeds and other natural plant foods found in shallow-water areas, including green-winged teal, gadwalls, wigeon and wood ducks, are typically the first to migrate, because they can quickly lose access to their food supplies during a sudden freeze.

The food resources used by migrating mallards, black ducks, scaup and other divers, which feed on waste grain in dry fields or on mollusks and crustaceans in deep, open lakes, are less vulnerable to cold weather. These birds don't have to migrate until deep snow covers the fields or frigid temperatures freeze big-water areas."

For waterfowlers who hunt along migration corridors, timing is everything. "To be successful at mid latitudes you have to be flexible enough to drop everything and go when the weather is right," Checkett says. "While I was conducting my master's research on state waterfowl areas in north-central Missouri, I noticed that new ducks would start to trickle in a day or two ahead of major cold fronts, and even more birds would pile into management areas as the front was blowing through. However, while the peak of the migration usually occurred with the front, the best hunting occurred on clear, cold days immediately after the front had passed.

"Migrating waterfowl take full advantage of tail winds," Checkett continues, "and many of the birds will ride them as far as they can until the wind shifts. On north-wind days, you'll often see a lot of ducks moving south, but many of them keep on going. From my personal experience, the best time to hunt is following a frontal passage, when the wind has just started to shift from north to the south. Migrating flocks know it's time to stop when they hit a headwind or the wind subsides."

At such times, Checkett recommends that waterfowlers use large decoy spreads and aggressive calling to draw in passing flocks. "Nearly all migratory birds use flocking as an adaptive strategy. When ducks first arrive in an area, they are often drawn to large wetlands in search of concentrations of other ducks that signify safety and the availability of food. New ducks respond to calling for the same reasons. It's no coincidence there is a strong duck-calling tradition in places like central Illinois, where great numbers of migrating waterfowl pass through each fall."

Winter (Dec. 16 - Jan. 30)

By the middle of December, most waterfowl have reached their wintering grounds across the southern tier of the United States and Mexico. Now, the most important biological need of wintering ducks, next to food and general survival, is selecting a mate. Although the timing varies by species, courtship activity generally increases throughout winter, and wintering waterfowl congregate in areas with an abundance of foods that will provide them with the energy they need to compete for mates.

The availability of waterfowl foods on many wintering areas is often determined by how much rain is received during the season. Heavy rainfall events can suddenly flood thousands of acres of productive new waterfowl habitat in agricultural fields and river bottoms, and dabbling ducks flock to these areas to exploit new food resources.

During the early 1990s, Dr. Bobby Cox, presently a waterfowl researcher with the U.S. Geological Survey, conducted a landmark studysupported in part by Ducks Unlimitedof movements of wintering pintails in southwest Louisiana. Cox and his colleagues marked nearly 350 hen pintails caught in October in a study area surrounding Lacassine National Wildlife Refuge and tracked them by ground and air through the end of February.

The researchers made some surprising discoveries. "We learned pintails that initially migrate to the Louisiana Gulf Coast often fly north into the Mississippi Alluvial Valley (MAV) of north Louisiana and Arkansas to meet approaching cold fronts and associated low pressure cells," Cox says. "This reverse migration appears to be triggered by a sharp drop in barometric pressure. This is likely a cue because, on average, it's at such times that the MAV receives heavy rains.

Another study conducted in the Central Valley of California produced similar results. This behavior doesn't appear to be unique to this area or to pintails. All dabbling ducks are constantly in search of newly flooded habitat because that is where food availability is highest."

In most cases, Cox's marked pintails migrated north on a strong south wind flowing up from the Gulf toward approaching fronts. However, in some cases, the birds actually bucked a north wind. "A lot of hunters wait for ducks to come down from the north on cold fronts, when in reality, depending on their location, they might actually receive more ducks from the south."

Food availability isn't the only factor that influences habitat selection by wintering waterfowl. Chad Manlove, manager of conservation programs at DU's Southern Regional Office in Jackson, Miss., explains, "Ducks become more secretive while selecting mates. They seek out wetlands with heavy cover, such as flooded buckbrush, timber, and emergent vegetation, where they can break up into small groups and conduct courtship displays. Once pair bonds are formed, ducks become even more reclusive. Pairs will often go out to feed with other ducks at dawn and dusk, but during the day, they look for places where they can isolate themselves, so the male doesn't have to expend energy protecting the hen from the advances of other males.

Of course, wetlands with heavy cover also provide waterfowl with good thermal cover, which is another means by which the birds conserve energy."

Waterfowl have few natural predators on their wintering grounds, and by late December and January, hunting is the principal cause of mortality for many duck species. Not surprisingly, hunting has a large impact on habitat selection among wintering waterfowl. Pintails, in particular, appear to modify their feeding and roosting habits in response to hunting pressure.

Cox recalls, "The Saturday before opening day in southwest Louisiana, which is the day most hunters in the region go out and work on their blinds, we started to see an increase in the number of pintails using Lacassine refuge during the day, and a lot of those birds also began to feed nocturnally. Once the season opened, we saw a big spike in the number of birds using the refuge during the day and then feeding at night in rice fields off the refuge.

During the split, when the hunting season was temporarily closed, diurnal use of the refuge dropped from roughly 60 percent of the marked birds to about 40 percent. However, as soon as the hunting season reopened, the birds quickly adjusted their schedules and again started using the refuge in higher numbers."

The lesson for duck hunters, according to Cox, is to manage hunting pressure wisely on wetlands and fields. "If you hunt any given area too much, in the long run you are going to have less success than if you hunt that area less frequently. It's hard for many hunters to grasp the concept that you will actually bag more birds by hunting fewer days."

Manlove, who hunts largely on public lands in the Mississippi Delta, scouts extensively during the off season to find remote sloughs and beaver swamps with limited access. "Now more than ever, hunting pressure is going to dictate success. Ducks are already looking for seclusion in winter to conduct pair-bonding activities, and hunting only magnifies this tendency. Today, ducks often won't use areas that are hunted more than once or twice a week. To find these places on public land, you have to be willing to walk a long way or ride for a long time in a boat to go where other hunters either don't know about or are unwilling to go.

Ducks are going to find these places and use them."

He adjusts his decoy spreads to match the behavior of ducks throughout the season. "As winter progresses and more and more birds have selected mates, I'll cut back on the number of decoys in my spread. By January, I use only six to 10 highly realistic decoys. I set them in pairs and as lone males, simulating ducks that have either formed pair bonds or are conducting courtship rituals. Also, motion in the decoys becomes critical late in the season, especially while hunting in sloughs that have thick cover and are sheltered from the wind. I use a jerk cord and kick water where I can to keep the decoys moving in a lifelike manner."

Manlove also calls more sparingly later in winter. "By the end of December, hunting pressure has made many of the birds extremely call shy. When ducks are working, I'll often only use a five-note greeting call and a few soft quacks and some feeding chatter to the let them know I'm there. You'll also see a lot of lone drake mallards in the winter, and the lonesome hen calla series of single quacks spaced a few seconds apartcan be absolutely deadly on these unpaired greenheads. Other times, particularly on calm mornings, it's best not to call at all and simply let motion in the decoys do the work."

Waterfowl biologists clearly have a unique perspective on hunting, derived from years of experience studying waterfowl in different environments. Renner provides some parting wisdom, "The key to success in any form of hunting is to know your quarry. All waterfowlers should take the time to learn as much about ducks and geese as they can. This will not only make you a more successful hunter, but it will also give you a greater appreciation for how these amazing birds interact with their environment."