Feeding Time

When I boat into a duck marsh in the fall, the water often looks like chocolate milk covered with the leaves and root material of various aquatic plants. Obviously, these are clear signs that waterfowl were feeding in the marsh at least part of the night. And studies confirm that during fall and winter waterfowl spend much of their time feeding. Movement from daytime loafing sites to nocturnal feeding locations is common in many waterfowl species, with daily weather and other environmental factors influencing how much waterfowl feed at night.

While there are no absolutes regarding the daily activities of waterfowl, research has revealed a variety of nocturnal feeding behaviors in ducks. Diving ducks on the Great Lakes, for example, take flight at dusk from open-water roosts and move to shallower near-shore areas to feed during the night. Mottled ducks spend more time feeding at night than during the day and move from deeper daytime habitats to shallower waters to feed at night.

But this doesn't mean that all waterfowl feed at night. Research has found that in many areas of the Mississippi Alluvial Valley, mallards spend much of the day feeding in flooded timber and roost elsewhere at night. In a study of diving ducks in the southeastern United States, buffleheads, lesser scaup, and ring-necked ducks fed more during the day than at night. Other work on northern-wintering sea ducks and mergansers showed virtually all feeding occurred during daylight hours. The same was true for Canada geese in the Upper Midwest. But contrasting results were reported for Canada geese in the East and in other parts of the Mississippi Flyway where nighttime feeding was common.

Management Implications

What waterfowl do at night is often a direct result of what happens during the day. Ducks and geese often respond to changing habitat conditions and disturbance by altering their behavior, especially their feeding activities, from day to night. For example, in areas with heavy hunting pressure, waterfowl often congregate in no-hunting zones during the day and then fly out to feed during the night before returning to rest areas before dawn.

Research examining the effects of disturbance on wintering waterfowl has largely focused on negative impacts on the birds' survival and body condition. If waterfowl have to expend more energy flying in response to disturbance, the daily cost in lost feeding time could have an impact on the birds' ability to acquire body fat for migration and breeding. In response, wetland managers usually provide more undisturbed feeding habitat for the birds in these areas.

Studying Nocturnal Behavior in Waterfowl

Much of the data needed to guide waterfowl management during migration and winter involves how, when, and where ducks and geese budget their time. To collect this behavioral data, researchers observe flocks or individual birds and record how much time they spend doing things like loafing, feeding, courting mates, swimming, and flying in different habitats. Of course, collecting data on waterfowl behavior is far more challenging at night than during the day. While radio transmitters and night-vision equipment have improved our ability to study the nocturnal activities of waterfowl, significant knowledge gaps still exist about what waterfowl do after dark.

Dale Humburg is chief biologist at DU national headquarters in Memphis.

As Different as Night and Day

Research shows that waterfowl behave differently before and after dark. Some interesting findings include:

• Waterfowl are typically more active at night in mild weather and curtail their nocturnal activity during severe weather.
• Waterfowl generally fly out to feed earlier in the evening on moonlit, windy nights than on moonless, calm nights.
• Pintails in south Texas and Louisiana feed largely at night in flooded rice fields and spend much of the day loafing in rest areas. Nearly all the pintails in one study delayed their departure until after sunset and traveled up to 15 miles in 30 minutes during evening feeding flights.
• In coastal areas, black ducks time their nighttime feeding activities to coincide with low tide when food availability is greatest.
• Gadwalls in Louisiana spend more time feeding and resting at night than during the day, primarily in response to harassment by avian predators, in this case northern harriers.