Family stability in greater white-fronted geese

I investigated the stability of parent-offspring bonds, and sibling-sibling bonds of neck-banded Greater White-fronted Geese (Anser albifrons frontalis) during winters (September-May) in California and southern Oregon from 1979 to 1989. Geese captured at feeding sites were more likely to be in social groups than those captured at roosting sites. Offspring remained associated with their parents longer than reported for other geese, as 69% of yearlings, 39% of two-year-olds, and 38% of three-year-olds and older were observed with their parents during winter. The proportion of time offspring spent with their parents declined as they grew older, being 76% for juveniles, 32% for yearlings, and 15% for two-year-olds and older. The prevalence of extended family groups was corroborated by counts of landing groups of unmarked geese. Sibling bonds also persisted after the first year of life, with 74%, 50%, and 39% of siblings maintaining some degree of social contact at ages of one, two and three years or older, respectively. Older offspring were more likely to associate with brood mates than with parents. Intensive observations ended when the oldest known-age geese were 34 months old. Incidental sightings in subsequent years revealed that some offspring up to eight years of age still associated with their parents and/or siblings. The benefits of maintaining long-term family bonds were not readily apparent, as there was no difference in the reproductive success of parents with and without attendant offspring, and yearlings that associated with parents were not more likely to survive than yearlings that did not associate with parents. However, older offspring and their parents may benefit by remaining together if extended families are more dominant and have better access to limited food and safe roost sites. Parents benefit if their fitness is enhanced due to nest defense provided by older offspring, and subadults probably benefit from staying with their parents by learning foraging and predator avoidance strategies from parents and older siblings.