In the migratory behaviour of the Barnacle Goose Branta leucopsis several changes have occurred over the past few decades. Barnacle geese breeding in Russia have delayed the commencement of spring migration with approximately one month since the 1980s, new populations have emerged in former stopover areas in the Baltic Sea region, and a non-migratory population has emerged in the wintering area in The Netherlands. This thesis aims to understand these changes. First, I studied the delay in commencement of spring migration. In the 1970s and 1980s, barnacle geese commenced spring migration half April, whereas spring migration now commences half May. I used a dynamic programming model to test three different possible explanations of delay in migration: 1) Climate change, because geese follow a green wave of fresh plant growth during spring migration, and are thus expected to be sensitive to increasing spring temperatures. 2) Competition for food during stopover because the population migrating to Russia has rapidly increased during the period in which the migration change occurred. 3) Predation danger during stopover because the number of avian predators such as White-tailed Eagles has drastically increased in the Baltic stopover area. The model showed that a delay of one month is adaptive in both the case of competition and predation danger. Strikingly, predation danger has received very little attention so far in goose studies. Migration strategy in geese is not genetically but culturally inherited, especially from parents to offspring via an extended period of parental care. Because this thesis focused on understanding migratory change, I focused on the parental care behaviour and the parent-offspring association because a change in migration was expected to be preceded by a change in the parent-offspring association. Because spring migration had delayed, the question arose whether the termination of parental care also had delayed. This would indicate a mechanistic link between the decision of commencement of ...