By Michael Schummer, Ph.D.
We've all been there, those days when you can pick your shots as greenheads hang over your decoys, wigeon dive recklessly into your rig, Canada geese are everywhere, and bluebills pile into your spread. But we've also had days when we stare at empty skies and the retriever curls up in the corner of the blind for a good nap. We are lucky, however, because the timing of waterfowl migration differs among species. The fall movements of ducks and geese occur from September through January, and most of us—no matter where and when we choose to hunt—are likely to witness an abundance of birds at least a few times each season.
Decreasing day length is the primary environmental cue that causes waterfowl to begin heading south from their breeding grounds in autumn. Shorter days indicate that worsening weather is not far behind, bringing wintry conditions that freeze wetlands and cover farm fields with deep snow. However, while day length ultimately stimulates migratory behavior, waterfowl movements are also influenced by weather and food availability.
Waterfowl and other birds use a variety of navigational cues during migration. These include the position of the sun and stars, the earth's magnetic field, and topographical features such as rivers, mountains, lakes, and coastlines. Collectively, these cues enable waterfowl to migrate even on the darkest nights.
There is an interesting behavioral difference between ducks, geese, and swans, in that the latter two groups of birds typically migrate in family units. Juvenile geese and swans follow their parents during migration, and in doing so they learn to recognize key landscape features along their migration routes to help guide their journeys. In contrast, young ducks do not usually have the benefit of their parents' experience in guiding migration. Most ducks do not have long-term pair bonds, and males usually abandon females late in the incubation period. Subsequently, females may abandon broods as the ducklings achieve flight stage and adult females are molting their flight feathers. Young ducks typically gather in flocks with other birds of their species before departing the breeding grounds, and are believed to use the same instinctive navigational cues that adult ducks use during migration.
The cues that trigger the spring migration are much like those used by waterfowl in autumn. Increasing day length indicates that it's time for the birds to start preparing for the long trip back to the breeding grounds. In preparation for the spring migration, waterfowl consume large quantities of certain foods in order to store fat as quickly as possible. For puddle ducks, these foods include native wetland seeds and, for species that field feed, agricultural grains. Conserving high-quality habitats that are used by waterfowl during this period is vital because food is particularly scarce during this time of year. Plants have not started growing yet, and much of the food that remains consists of "leftovers" from the previous growing season.
Once the birds have acquired enough fat, and day length has surpassed a certain threshold, migratory restlessness known as zugunruhe occurs, and with a favorable wind, waterfowl take flight for their breeding grounds. Unlike during the fall migration, when weather does not prevent waterfowl from moving southward, snow and ice can be a substantial barrier to the birds' journey north. Waterfowl often must stage for several weeks before the next warm front makes habitat available as snow and ice retreat northward. These stops along the snow and ice line are crucial periods for waterfowl, as the birds must feed heavily to ensure that they retain enough fat to fuel the next leg of the migration. For waterfowl enthusiasts, the spring migration is a prime opportunity to observe spectacular concentrations of ducks, geese, swans, and other migratory birds on national wildlife refuges, state wildlife areas, and privately owned wetlands.
Eventually, using the same navigation strategies that were used in autumn, waterfowl will return to their breeding grounds. Remarkably, geese will find their way across the sprawling Boreal Forest to the same breeding colonies in the Arctic, and some female puddle ducks will even home back to the same patches of grassland where they nested successfully in previous years. This truly speaks to the capacity of waterfowl to navigate using the stars, the sun, their internal compasses, and simply their memory of prominent landmarks. It also reminds us that conserving vital waterfowl habitats across the birds' continental ranges is essential to ensuring that ducks and geese return "home" to breed and produce offspring that will ultimately join the fall migration. Soon the cycle will start all over again, much to the delight of hunters and everyone who admires these magnificent birds.
Dr. Michael L. Schummer is a visiting assistant professor of zoology at the State University of New York (SUNY) Oswego and Roosevelt Waterfowl Ecologist at the SUNY College of Environmental Science and Forestry.
Weather and Waterfowl Migrations
Researchers recently investigated various weather conditions that influence puddle duck migrations and discovered that the combination of decreasing temperature and increasing snow cover best explained the birds' movements in autumn. The only outlier was the blue-winged teal, which migrated mainly in response to decreasing day length. This makes sense because the primary breeding area for this species—the Prairie Pothole Region—is subject to early freezes and snowfall, and most bluewings winter far to the south in Mexico, Central America, and the Caribbean. Thus, once the breeding season is over and blue-winged teal are fat enough to make the journey, these ducks depart for their neotropical wintering grounds.
The research also confirmed what many hunters already know—that American green-winged teal are the next ducks to migrate, followed by northern shovelers, American wigeon, and gadwalls. Northern pintails make their move later in the fall, and the last species to arrive on their wintering grounds are mallards and American black ducks, which often remain in northern and midlatitudes, at least for a while, even when snow and ice cover the landscape.
A common question posed by waterfowlers is, "Has fall weather become milder in recent years?" The short answer is yes. From 1980 to 2014, the trend has been for milder weather across much of the United States. This may explain why, in recent years, many hunters in southern latitudes have noted that puddle ducks seem to be showing up later than in the past.