Adoption of non-related goslings and intergenerational family cohesion among Greenland White-fronted Geese (Anser albifrons flavirostris)

Greenland White-fronted Geese Anser albifrons flavirostris exhibit prolonged parent–offspring and sibling–sibling associations, suggesting fitness advantages to such behaviour, so we used reduced representation genome sequence data to determine the degree to which marked flock members observed associating in apparent parent–offspring and sibling–sibling relationships in the field were genetically related. Among 50 bled, marked and released geese, we genetically identified members of 11 different family groups, confirming all observed male parent–offspring relationships as genetically predicted, but only 10 out of 12 (83%) possible female parent–offspring relationships (i.e. two offspring were not genetically related to the adult female in their family groups observed in the field); these two ‘adopted’ offspring were responsible for four (15%) of the cases where observed ‘siblings’ were not genetically related to other family-member first-winter birds with which they associated. One multigenerational family consisted of three genetically confirmed grandmother–mother–sibling offspring relationships, not previously reported in arctic-nesting geese, as well as one of the two ‘adopted’ first-winter geese.