by Dale Humburg
You'd think a marsh would be a serene and peaceful place after dark. But having spent a few nights trying to sleep in a duck boat, I can assure you this isn't the case. With the frequent whistling wings of ducks overhead, the incessant clucking of coots, and the din of migrating snow geese—not to mention the muskrat on the bow of the boat eating a cattail tuber—I found the marsh to be quite an active place at night.
And on many occasions, I've left a marsh late in the day with hardly a duck in sight only to return to the same spot early the next morning and flush what seemed like half the flyway's birds ahead of me. These mysteries raise questions like "where were the birds yesterday, when did they arrive, and what were they doing all night?"
Migrations and Local Movements
Most waterfowl migrations occur at night. Studies indicate that migratory movements intensify shortly after sunset, peak in the middle of the night, and decline thereafter. The result can be an impressive increase in local waterfowl numbers overnight. These nocturnal migrations often explain why a marsh can be void of waterfowl one afternoon and then teeming with birds the next morning.
But waterfowl also make shorter, local movements at night. On migration and wintering areas, the daily activity of ducks and geese is influenced by the birds' energy demands, weather and habitat conditions, and disturbance from hunters or natural predators. Being highly mobile, waterfowl respond quickly to changes in their environment by moving from one habitat to the next. And ducks and geese often make these local shifts in distribution at night.
Loafing and Roosting
Waterfowl spend many hours a day loafing, sleeping, and performing basic maintenance and comfort movements like preening and stretching. The birds select loafing and roosting sites based on the temperature, humidity, wind speed, and sky conditions. On warm, sunny days, for example, ducks and geese will loaf in open areas where they can warm themselves in the sun. At night, waterfowl often roost in more sheltered habitats where the birds can conserve body heat and save energy. By moving among a variety of different loafing and roosting sites, the birds can maximize their energy savings under different weather conditions and at different times of day.
Habitat selection is especially important for waterfowl during extended periods of unfavorable weather when even big ducks like mallards and black ducks have to rely on stored fat reserves to survive. Energy costs to waterfowl are highest on clear nights when heat loss is greatest in open habitats. On cloudy nights, differences in heat loss are less pronounced among different habitat types.
Studies conducted in the Mississippi River floodplain showed that, at the same temperature, flooded willow wetlands with dense woody cover provided a more favorable microclimate for roosting ducks than flooded corn or deep-water habitats. At night, the closed canopy of flooded willows shielded the birds from heat loss as well as avian predators like great horned owls.
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.
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.