By Mike Brasher, Ph.D.
Experienced waterfowl hunters know that ducks respond differently to calling throughout fall and winter. Although habitat conditions, weather, and local hunting pressure can also play a role in the birds' willingness to decoy, courtship and pairing activities are responsible for many of the changes in waterfowl behavior observed during hunting season. Understanding these behaviors is not only enlightening from a biological standpoint, but also necessary for developing responsible harvest regulations and may even help hunters bag more birds.
A quick refresher on waterfowl mating systems is needed to appreciate the significance of courtship and pair formation to waterfowl. All waterfowl are essentially monogamous, meaning one female will pair with only one male. Geese, swans, and whistling ducks are classic examples of species that form lifelong pair bonds (perennial monogamy), while most species of ducks form pair bonds that last only four to eight months, often with a new mate each year (seasonal monogamy). As a result, most ducks undergo courtship and pair formation annually, while geese, swans, and whistling ducks do so only when acquiring a mate for the first time, when a mate dies, or in rare instances when paired birds become geographically separated.
PAIRS, HARVEST AND MATE LOSS When a paired bird is harvested by a hunter, its mate must find a suitable replacement. Most waterfowl establish new pair bonds within days or weeks after losing a mate, but the timing of the loss can have an impact on the birds' survival and productivity. In recent studies, female black brant that lost mates during the hunting season subsequently found new ones, but experienced higher mortality than birds that did not lose mates, likely because of a greater vulnerability to harvest and predation during the courtship and pairing process. In another study, researchers used controlled experiments to demonstrate that among female mallards, the loss of a mate in late winter may reduce annual recruitment by as much as 7 percent. The increased time and energy costs associated with finding a new mate were believed to have been responsible for the decreased productivity in these birds. This information is vital to ensure that hunting season dates and lengths are rooted in science and compatible with the reproductive behaviors of waterfowl populations. Rigorous consideration and application of the latest scientific findings will help waterfowl managers maintain healthy populations of ducks and geese for future generations to enjoy.
A defining characteristic of seasonal monogamy is the weakening of pair bonds during summer as female ducks nest and begin incubation. Previously paired males leave the breeding grounds for traditional molting sites while females incubate their eggs and raise their broods. During fall, large concentrations of ducks gather on staging areas and eventually begin their southward migration. It is during this time that the annual pair-formation process begins. Although the exact timing varies among species, courtship activity in ducks starts gradually on northern staging areas and ultimately reaches a fever pitch during winter and early spring at middle and southern latitudes. If you have ever wondered why ducks don't respond as well to calling early in the fall as they do later in the season, now you know the reason.
The pattern of early pairing for ducks is unique in the bird world, as most species of seasonally monogamous birds, such as migratory songbirds, delay courtship and pairing until spring or summer. This has been a topic of much study and debate among biologists. Attempts to explain this behavior have relied heavily on comparisons among species and taxonomic groups.
As a general rule, dabblers tend to pair earlier than divers, but variation exists even within these groups. Mallards, American black ducks, and gadwalls are among the earliest dabbling ducks to establish pair bonds, with approximately 75 to 80 percent of females pairing by late November. In contrast, the majority of female American wigeon, shovelers, and green-winged teal do not establish pair bonds until late January or February. As winter progresses, pairing opportunities for males quickly diminish, which helps explain why a well-timed hen mallard decrescendo call can be irresistible to a lone greenhead flying overhead in January. Divers are the last of the ducks to establish pair bonds, which typically occurs in late winter or spring and may continue until the birds arrive on their breeding grounds.
This information is vital to ensure that hunting season dates and lengths are rooted in science and compatible with the reproductive behaviors of waterfowl populations. Rigorous consideration and application of the latest scientific findings will help waterfowl managers maintain healthy populations of ducks and geese for future generations to enjoy.
Early pairing is believed to benefit female waterfowl in several ways. Pairs are dominant toward unpaired birds, and paired males protect their mates from being harassed by other males. As a result, females that pair early likely gain access to higher-quality foraging habitat and have more time to acquire nutrients and fat reserves than unpaired females. Early pairing may also give females more time to assess potential mates and develop a strong pair bond so nesting can begin soon after the birds arrive on their breeding grounds. This is advantageous because early-nesting hens generally are more productive than later nesters.
Most duck populations consist of a higher number of males than females, creating fierce competition among drakes for mates. Consequently, males also stand to benefit from early pairing by securing a mate while more unpaired females are available. Within species, it is well documented that older, more dominant birds pair earlier. This occurs because older birds are usually larger and in better condition, and have more experience competing for mates. However, finding a mate doesn't come without risk. The rigors of courtship, pair formation, and mate defense are energetically costly to males and may expose them to increased risk of predation.
Patterns of pair formation in geese and swans are less complicated than those in ducks, primarily because geese and swans form lifelong pair bonds. Although reproduction in geese usually does not occur until the birds are three or four years old, young geese frequently engage in courtship and pair formation behaviors well before they are sexually mature. These short-lived initial pair bonds are believed to provide young geese with experience that will help them find mates when they are older. The timing of courtship and pairing among geese and swans also varies by species, but generally occurs during winter or spring, as it does in ducks.
While sometimes overlooked, courtship and pair formation are of great importance to waterfowl populations. These behaviors enable male and female waterfowl to select suitable mates and begin the reproductive process, which is essential to the survival of their species. The next time you are in the marsh, make an effort to observe the interactions between male and female waterfowl. You might even witness some of the fascinating courtship displays used by males to gain the attention of a nearby female. If you do, you're sure to be entertained.
Based in Lafayette, Louisiana, Dr. Michael Brasher is biological team leader for the Gulf Coast Joint Venture.
Fowl Fact: IRRECONCILABLE DIFFERENCES Researchers have noted cases of "divorce" in geese, in which paired birds voluntarily go their separate ways. Divorce has been observed in pairs that were not successful during a nesting attempt or in laying and hatching eggs.