Canada geese are different. Pairs will typically remain together throughout the birds' lives. But this isn't absolute. In some cases, Canada geese will seek a new mate while their former mate is still alive. This typically occurs when one member of a pair is injured or becomes lost during migration or on the wintering grounds.
A significant difference between geese and ducks is that the goose family structure remains intact throughout fall migration, winter, and spring migration. The family breaks up only after the birds return to the breeding grounds and the adult pair begins to actively nest. At this time, the yearlings join flocks of other nonbreeding geese. When these young birds are two or three years old, they will find their own mates on the wintering grounds. The new pairs then follow the same adult life pattern described above. This is referred to as perennial monogamy whereas mallards demonstrate seasonal monogamy.
The other mating system known to waterfowl—polygamy—has been observed in only a few species. Forms of polygamy include polyandry (single females have several male mates) and polygyny (single males have multiple female mates). Polyandry has never been observed in waterfowl, but polygyny occurs in some species. In North America, the ruddy duck and muscovy typically do not form pairs at all. In these species, the male establishes a territory that he defends from other males but allows females to enter. Some males have the opportunity to breed with more than one female in their territory, thus illustrating one form of a polygynous mating system.
Waterfowl mating behavior varies considerably based on the birds' needs. For some ducks like the northern shoveler, defending a feeding territory is a dominant concern. For others, like the northern pintail, protecting hens from harassment by unpaired males may be critical. And for most geese, cooperation in all phases of family life is important to the birds' survival. So this spring, when you see a pair of ducks in a local wetland—perhaps mallards or blue-winged teal—see if you can figure out how the drake and hen are cooperating to maximize the success of the upcoming breeding season.
Mating Systems and Variation in Canada Geese
The family structure and mating systems of Canada geese are directly responsible for the existence of different races of these white-cheeked birds. When young geese form pairs of their own, they choose mates from flocks of young birds from the same areas where they were raised. Thus, the characteristics of their respective parents that were molded by local conditions are propagated in their own young—much like line breeding in dogs.
In this way, distinct localized populations have developed over thousands of generations, which we can see in the size, coloration, and conformation of each race. For example, southern giant Canada geese have large bodies, long necks, and generally light-colored plumage. In contrast, Canada geese that nest in the high eastern Arctic are much smaller, have shorter necks, and generally darker plumage. Since each population tends to return to its traditional breeding and wintering areas, biologists can manage the harvest of each population from these distinct locations separately.