Why do geese and swans usually maintain long pair bonds?

Geese and swans maintain long-term pair bonds primarily because their reproductive success and the survival of their offspring are enhanced by the care provided by both parents.12

In many bird species, including most Anseriformes, monogamy is favored when environmental resources are limited and the maximum survival of the young requires the investment of both the male and the female. Unlike many duck species, where the male often deserts the female after incubation begins, male geese and swans remain with the female and their family throughout the breeding and rearing process. This biparental care is crucial for the protection and guidance of the young, which remain with their parents during their first winter and migrate in their company.132

Furthermore, the Anserinae subfamily—which includes swans and typical geese—is characterized by this extended family life and social behaviors, such as the "triumph" ceremony, which help reinforce these stable, long-term pair bonds.42